Fix deprecated accelerator call
Fix the following deprecated gtk call:
gnomemusic/window.py:72: DeprecationWarning: Gtk.Application.add_accelerator is deprecated
app.add_accelerator('<Primary>a', 'win.selectAll', None)
Fix the following deprecated gtk call:
gnomemusic/window.py:72: DeprecationWarning: Gtk.Application.add_accelerator is deprecated
app.add_accelerator('<Primary>a', 'win.selectAll', None)