This commit creates a new "frontends/lyx_gui.C" that contains all functions that...

This commit creates a new "frontends/lyx_gui.C" that contains all functions that are not frontend dependent any more. It also creates 3 new pure virtual methods in Application:

virtual std::string const romanFontName() = 0;
virtual std::string const sansFontName() = 0;
virtual std::string const typewriterFontName() = 0;

My goal is to transfer all of "frontends/*/lyx_gui.C" to "frontends/lyx_gui.C". When this is done, "frontends/lyx_gui.C" can go altogether as its functions will then be replaced with direct calls to theApp->XXX().

* frontends/lyx_gui.C: new file with code transfered from [qt3,qt4,gtk]/lyx_gui.C

* frontends/Application: 3 new font related pure virtual methods

* [qt3,qt4,gtk]/GuiApplication: implement the above method with code transfered from lyx_gui.C

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15208 a592a061-630c-0410-9148-cb99ea01b6c8