Adding rendering for historic=city_gate

[jragusa]

Fixes #152

Changes proposed in this pull request:
Show an icon and label for historic=city_gate in man_made colour

Test rendering with links to the example places:
https://www.openstreetmap.org/way/317181351
Before

After

[kocio-pl]

Thanks, good to see this code!

I just think it makes more sense to move it to z17+, because it can be a part of something bigger and should not appear too early - that's why I pushed defensive towers there to not compete with castle for example, see this location:

z15

z16

z17

[jragusa]

Fixed

That should be correct now.

Oups: it's "shift" in the commit...

[kocio-pl]

You can try squashing commits into one by the way. There are multiple guides for this, like:

https://gist.github.com/patik/b8a9dc5cd356f9f6f980

but I do it with GUI called gitk under Linux. I make soft reset to the place right before my changes, so the commits are rolled back, while changed files are still there. Then I leave this app, make git add . and make new commit which holds all the changes. Then I push them with -f (force) option.

Quite easy and safe.

[jragusa]

Done

I forgot that we can squash commits. Thanks to notice me @kocio-pl

[kocio-pl]

Thanks, it's good to see some of the oldest tickets going away...