Themable compiler output in message window (GTK version)

[Rakksor]

A version of pull request #1377 that uses the GTK theme instead of the geany colorschemes to customize the colors of the compiler output in the message window.

[elextr]

Its great that you thought to do the docs, but you forgot to change them to the GTK way 😄

[Rakksor]

Damn, missed that. 😊
I just removed it for now without documenting the new stuff, since styling the tabs etc. isn't documented either.

[codebrainz]

@Rakksor nice work. I will try to test and merge this weekend if I get time.

We should probably squash the (now) unrelated commits so we just get the changes in 33a8cc9. @Rakksor if you want to do it ahead of time, it will make merging it a little easier.

[elextr]

Works for me, not depending on the theme colours is the way to go.

@codebrainz do not merge this until the documentation is done, which as @Rakksor said depends on #1380 but as discussed on IRC @b4n is gonna look at that soon :)

[Edit: to be clear, #1380 should add a section to the manual documenting the tab names, and then these names just get added to that section]

Also @b4n should probably approve GTK fixes :)

[codebrainz]

See #1382

[Rakksor]

Closed since this has been included in #1382