Fix compile error on Mac < QT 5
Flat Titlebar not supported on QT < 5 on Mac
Merge pull request #898 from Joern-R/pull

Translation Enablement
Adjustment proposal - DWM support for for Color Setting (CCHROME)

... gcconfig.pri.in + src,pro -> same logic as for other additional libs
+ setting the variable GC_...
... Colors.CPP -> changed location to get the DWM color to use in
"menuBar" of MainWindow
+ add comments of what is still not working (don't want to mess up
something)

(cherry picked from commit 6f39fc9d305098177ead42c331a55ea85a68270f)