Finally sanitizificat0red the mess and #ifdef hell with main.cpp, Global:: and friends

This replaces #ifdefs mostly by OO stuff, i.e. we now have a class hierarchy in place
for initializing the application. Also, namespace Global:: is gone[1]; most of its functionality
is part of the new Quassel object now which encapsulates common app stuff.

You should clean (rm -rf) your build dir, as these changes are quite invasive.

[1] Some remnants are still there until I get around to redesigning genversion, and actually
    fill Quassel::buildInfo() with data.