Switch to GDK_KEY_*
Remove gdk threads
Switch to newer API for gps input sources
Rename custom functions to prevent GTK 3 conflicts
Get rid of GtkNotebookPage references

We convert these to gpointer and don't use them because the API is
different between GTK 2 and GTK 3.
Convert GtkBox and GtkScale to GTK 3 version

Also add a wrapper to keep the GTK 2 version compiling.
Fix build with GTK 3

This mostly just comments out some deprecated functions. They're not
particularly necessary so, but it would be good to find replacements
eventually.