This will be added to a ListBox with the volume controls. Expanding the
row will enable ReplayGain and give the user a menu to select ReplayGain
mode.
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>
This includes a set of Gtk.CheckButtons to choose what ReplayGain mode
to use, and a Gtk.Switch to enable or disable ReplayGain
Implements: #46 ("Create new Volume controls")
Implements: #48 ("Implement Intelligent ReplayGain")
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>