Enhancement trigger event when playhead moves

I introduced a new event, called repaintcurrenttime, which is triggered every time the current time playhead (the red, vertical line displaying the current time) is repainted.

This repaintcurrenttime event has been added to the documentation as well.
I also added a simple but relevant example of a use case for this event which can be found in example29_follow_the_playhead.html

In example 29 there are two timelines: one with the default playhead behavior that moves as time passes and another example where we listen to the repaintcurrenttime event and make the timeline move while the playhead stands still.

I think this example is relevant and this feature is useful because it can be found in some products (for example some video editors move the timeline instead of moving the playhead). Also, I recently had to implement this functionality because there was a need to allow the users to monitor current events without having to move the timeline (with the default behavior, and without moving the timeline, the playhead would eventually disappear from the screen and the users would no longer be monitoring the current events). These events the users have to monitor come from a server and are dynamically added and their state is changed and that is why this feature is useful in that scenario.

Thank you for your time!