overrides for message-dialog, window, tree-view and tree-store with relatives

With this I provide all overrides necessary to migrate all existing opine widgets to gir-ffi-gtk3.
You may want to give me commit access to the repository as I expect to maintain much of the codebase while giving life to opine.

Enjoy,
Patrick

Sorry, dumped gir_ffi-gtk out of opine mostly due to #15, the license and the overall status of the project, so Im dead on this one.