Gtk+ improvements

- move gobject-glue inside gobject
- handle gdkevent type
- add an example

The GdkEvent handling is not like we wanted because the dispatch on the result of a function wasn't working like expected. (The idea was to dispatch on the gtype, with value g-type-from-name("GdkEvent"))

The application is a simple converter between celsius and fahrenheit, but it uses callback, dispatch and properties.