[gtk3] port mainwindow.py to GtkBuilder
@stephane.maniaci
Submitted by Stéphane Maniaci Assigned to Stéphane Maniaci @stephane.maniaci
Description
The main window of PiTiVi use a bunch of handmade Gtk code. Move Gtk actions/widgets into a builder file will greatly ease the transition process to GTK+3.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=655436