Initial commit of the new code.

Initial commit of the new code.

This mostly acts as a proof of concept for the following implemented features:
 - Generic GValue C++ wrapper.
 - Better support for setting/getting GObject properties.
 - Connection of arbitrary class member functions to GObject signals knowing
   only the signal name as a string, with conversion to/from GValue at compile
   time (using templates) and with actual type checking at runtime.

This is not yet meant to be a replacement for the old code, but it will
slowly evolve into that.