Log Message:
Update to 1.20.0:

gvc-applet: don’t try to increase refcount of a NULL object
gvc-combo-box: fix signal arguments
applet: restore icon for “Sound Preferences” menu item
avoid deprecated gdk_screen_get_height
applet: use GdkSeat with GTK+ >= 3.20
applet: make keyboard work in popup
gtk 3.22: avoid deprecated gdk_screen_get_monitor… functions:
refresh tray icon on icon theme change
mixer-dialog: remove style class .frame from a scrolledwindow
volume-control-dialog: avoid deprecated GtkAlignment
applet: show volume in popup even when muted
applet: improve volume increments
enable deprecation warnings by default
Translations update