Add a new member to FontInfo denoting the color to be used when painting.

* rowpainter.cpp: now the color for painting selected text and changed text is set via FontInfo::setColor. However, this color should remain a ColorCode as this color is used in e.g. the GuiCharacter dialog and for LateX output. Therefore I use now the FontInfo::setPaintColor function.

* FontInfo.cpp/h: new members paint_color_ and setPaintColor(). The function realColor is updated to return the paintColor when it is set.

See:
http://thread.gmane.org/gmane.editors.lyx.devel/114189

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@28422 a592a061-630c-0410-9148-cb99ea01b6c8