Add with-gdk-lock macro

The gdk-threads-enter and gdk-threads-leave functions are deprecated, now all
GDK and GTK+ calls should be made from the main thread.

See:
https://developer.gnome.org/gdk3/stable/gdk3-Threads.html#gdk-threads-enter
Add remaining functions to gobject-glue

* signals
* constructor/finalizer
Merge pull request #32 from fracek/gobject-glue

Gobject glue