Deprecate many legacy event signals

Deprecate many legacy event signals

Mark the following signals as deprecated:
event, event-after, button-press-event, button-release-event,
touch-event, scroll-event, motion-notify-event, enter-notify-event,
leave-notify-event, property-notify-event, selection-clear-event,
selection-request-event, selection-notify-event, selection-received,
selection-get, proximity-in-event, proximity-out-event. Most
of these have suitable replacements in event controllers and
gestures already. The selection-related signals will soon be
irrelevant when selection handling moves to GDK.

Set G_ENABLE_DIAGNOSTIC=1 to see deprecation
warnings for uses of these signals.