clock: remove deprecated g_type_init
clock: remove deprecated include
clock: don't use deprecated GtkSymbolicColor
ditem-editor: replace gtktable with gtkgrid
notification_area: fix deprecated warnings
panel: create better applet id
panel: fix panel properties
libpanel-applet: show applet edit menu popup on correct screen
Multi-monitor fix

 * In a multi-monitor setup, the main menu opens upward if the applet is in the
   bottom half of the screen, and downward if the applet is in the upper half of
   the screen. (And similarly for left/right.)
 * Solution: the menu should open towards middle of the *monitor*, not the
   *screen*.
move panel-separator to separator-applet
panel: fix background drawing