added several new event types that can trigger global animations

This change adds the following new global animations event types,
which can be used like the already existing "click:anim_X.part_Y":

* init:anim_X.part_Y  - triggers when animation is initialized
* start:anim_X.part_Y - triggers when animation is started
* end:anim_X.part_Y   - triggers when animation ends
* post:anim_X.part_Y  - triggers when animation post delay ends

The second part ".part_Y" is optional; if missing, events for every
animation part will trigger the animation for which this event is
defined.

The "init" event will trigger even if the animation is not yet
displayed, but starts waiting for its "init_delay" or "init_event",
while the "start" event will trigger when the first frame of the
animation is displayed.

The "end" event will trigger when the last frame of the animation is
displayed (either because the animation has stopped due to a click
event, due to the "anim_delay" being finished or because the animation
has completely moved off the screen), while the "post" event will
trigger when the "post_delay" is completely finished.