We also clean up some old references to the old G prefixed GUI classes
This also fixes a potential bug with using: C_OBJECT_ABSTRACT(GAbstractButton)
instead of C_OBJECT_ABSTRACT(AbstractButton)
Now it actually defaults to "a < b" comparison, instead of forcing you
to provide a trivial less-than comparator. Also you can pass in any
collection type that has .begin() and .end() and we'll sort it for you.
