Replace all color inheritances with explicit definitions (#121)

This commit implements a change for the meta-issue GH-120 that collects
and aggregates all information regarding the problems related to
"randomly breaking syntax highlighting".
There is an continuously increasing amount of issues related this bug
were the root cause is still a mystery.

The following timeline shows the problem based on reported issues in
this repository.

>>> 2019-07-31 - First breakages of Go & JavaScript syntax since IDE
                 versions 2019.2.x

The first cases are documented in GH-69 & GH-77 where the syntax
highlighting of some Go & JavaScript elements were wrong after updating
to IntelliJ version 2019.2.0, the update that introduced support for 20+
languages [1] out-of-the-box by integrating TextMate [2] schemes.

It resulted in a change for some Go & JavaScript editor color scheme
keys that previously inherited the best matching global keys, but used
the attributes defined by the parent theme "Darcula" after the update
instead. Therefore Nord's highlighting for Go & JavaScript broke and
required to explicitly define the values for the some attributes
(merged in GH-70 & GH-78) in order to achieve the same highlight like in
previous versions:

A comparison of the changes between Nord plugin version 0.6.0 and 0.7.0
[3] shows that there were absolutely no changes to the editor color
scheme related to the highlighting of Go & JavaScript code.
To this time the guess was that the root cause was the integration of
"TextMate" themes and the "fixes" have been released in version 0.8.0
[4].

>>> 2019-12-02 - Second breakage of Go syntax since IDE versions
                 2019.3.x

The second case is documented in GH-108 where the syntax highlighting of
some Go elements were wrong again after updating to IntelliJ version
2019.3.0. A comparison of the changes between Nord plugin version 0.8.0
and the time the issue was created (2019-12-02) [5] shows again that
there were no changes to the editor color scheme related to the
highlighting of Go code.

An interesting observation was that the wrong highlighting could be
fixed by disabling and enabling the Nord plugin again without restarting
the IDE (deny/postpone to later when the question dialog shows up).

Again, the "fixes" were then released in a the new plugin version
version 0.9.0 [6].

>>> 2020-01-28 - Another breakage of JavaScript & TypeScript syntax in
                 IDE versions 2019.3.x

On 2020-01-28 a new issue has been created that describes the breakage
of the syntax highlighting for JavaScript as well as TypeScript (which
inherits values from the JavaScript editor scheme keys) in GH-115.
This is really strange since the affected elements were fixed in GH-78
[7] to mitigate the first breakage!
To fix the problem again, the color definitions were then defined
explicitly in GH-116 [8] instead of relying on the non-working
inheritance of other theme keys.

The comparison of the changes between Nord plugin version 0.9.0 and the
time the issue was created (2020-01-28) [9] again showing that there
were no changes to the highlighting of JavaScript or TypeScript syntax
elements in the editor color scheme.

It was also possible again to temporarily work around the problem by
re-enabling or even re-installing the plugin. This definitely shows that
the root cause must be somewhere in the way the IDE loads themes and how
editor color scheme keys are inherited from other keys.

Again, the "fixes" were then released in a the new plugin
version 0.10.0 [10] on 2020-02-11.

>>> 2020-02-11 - Now PHP and general "markup" languages are also
                 broken...

The latest case occurred only several hours after [Nord plugin version
0.10.0 [10] was deployed and made public through the "JetBrains Plugin
Marketplace". This time the highlighting of strings and comments in PHP,
Markdown font styles (bold & italic) as well as other elements of
"markup" languages are broken.

Again, a comparison of the changes between Nord plugin version 0.9.0 and
0.10.0 [11] shows that there no changes to the highlighting for editor
color scheme keys for PHP, Markdown or any "markup" languages or
"Language Default" styles.

During the testing of Nord plugin version 0.10.0, that was released to
fix the problems of the broken JavaScript & TypeScript highlighting,
there were no problems regarding "markup" styles and all elements were
working fine in Markdown files.
Right after deploying the plugin to the "JetBrains Plugin Marketplace",
the highlighting suddenly broke "out of nowhere" after updating the
plugin for my IntelliJ.

>> Conclusion

These random breakages "drive me nuts" and it's frustrating as a theme
author to no being able to track down the root cause. Since the problem
occurs randomly, but can also be temporarily mitigated through one or
more plugin re-activation or re-installations, the problem origin must
be a bug in the IDE itself.

>> Mitigation Steps

This commit implements a workaround to prevent more styles from
breaking. It replaces all editor color scheme keys that inherit values
from other keys with the explicit style definitions instead.
This causes the code of the editor scheme to increase drastically due to
duplicate and repeated styles, but it currently the only way to work
around this non-working style inheritance in the IDE theme API.

[1]: https://www.jetbrains.com/idea/whatsnew/#v2019-2-editor
[2]: https://macromates.com
[3]: https://github.com/arcticicestudio/nord-jetbrains/compare/master@%7B2019-05-23%7D...master@%7B2019-07-16%7D
[4]: https://github.com/arcticicestudio/nord-jetbrains/releases/tag/v0.8.0
[5]: https://github.com/arcticicestudio/nord-jetbrains/compare/v0.8.0...develop@%7B2019-12-02%7D
[6]: https://github.com/arcticicestudio/nord-jetbrains/releases/tag/v0.9.0
[7]: https://github.com/arcticicestudio/nord-jetbrains/pull/78/files#diff-1146aace8d65c51b72c60139418ad4d0R1016-R1018
[8]: https://github.com/arcticicestudio/nord-jetbrains/pull/116/files#diff-1146aace8d65c51b72c60139418ad4d0R1118-R1133
[9]: https://github.com/arcticicestudio/nord-jetbrains/compare/v0.9.0...develop@%7B2020-01-28%7D
[10]: https://github.com/arcticicestudio/nord-jetbrains/releases/tag/v0.10.0
[11]: v0.9.0...v0.10.0

Related to GH-69, GH-70, GH-77, GH-78, GH-108, GH-109, GH-115, GH-117,
           GH-119
GH-120