Implement optional profiling for export

[MoritzBrueckner]

Linked to armory3d/armsdk#16.

Combined with the PR above, you can now choose to run cProfile when exporting the scene. This will generate a file called profile_exporter.prof in the SDK directory with detailed information about the number of calls and the time taken by the functions called during export. This file can then be opened by tools such as SnakeViz to get a graphical representation of whats happening during export:

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Example use case:

This is the result when compiling the celshade example project, which takes a huge amount of time. About 3/4 of the time are taken away for the export of individual objects (and analyzing the results a bit more leads to the conclusion that the way bone animations are exported is horrendously slow because for each bone the entire scene is set to each frame resulting in a complete redrawing and recalculation of the scene).

This is a very small step for the Python side of things towards #870. The new Profile context manager can be used for other occasions as well and can even be nested, although it will mess a bit with the results. It should always be opt-in due to performance reasons.

I've also added a new util function to get a preference setting or a default value if it doesn't exist, which makes many of the current get_[something]() functions obsolete (they are still used though, that's not part of this PR).

[luboslenco]

Thanks!

the way bone animations are exported is horrendously slow because for each bone the entire scene is set to each frame

Yes it's very ugly, unfortunately I am not aware of other way. :(

[MoritzBrueckner]

I thought about manually iterating through the fcurves and combine the individual transformations to matrices, but I don't know if that works. First I have to understand Blender's animation system better. Would be really nice if Blender had a way to retrieve the matrices for arbitrary frames.