timeline: Add repeat-count

Being able to easily set the number of repeats has been a request for
the animation framework for some time now. The usual way to implement
this is: connect to the ::completed signal, use a static counter, and
stop the timeline when the counter hits a specific spot.

In the same light as the :auto-reverse property, we can make it easier
to implement this common functionality by adding a :repeat-count
property that, when set, limits the amount of loops that a Timeline can
perform before stopping itself.

In fact, we can implement the :loop property in terms of the
:repeat-count property just by using a sentinel value mapping to
"infinity", and map loop=FALSE to repeat-count=0, and loop=TRUE to
repeat-count=-1.

doc/reference/clutter/clutter-sections.txt

@@ -718,8 +718,8 @@ clutter_timeline_clone
 <SUBSECTION>
 clutter_timeline_set_duration
 clutter_timeline_get_duration
-clutter_timeline_set_loop
-clutter_timeline_get_loop
+clutter_timeline_set_repeat_count
+clutter_timeline_get_repeat_count
 clutter_timeline_set_delay
 clutter_timeline_get_delay
 ClutterTimelineDirection
@@ -727,6 +727,8 @@ clutter_timeline_set_direction
 clutter_timeline_get_direction
 clutter_timeline_set_auto_reverse
 clutter_timeline_get_auto_reverse
+clutter_timeline_set_loop
+clutter_timeline_get_loop
 
 <SUBSECTION>
 clutter_timeline_start