Pause and restart animations

[minimav]

Currently it is only possible to start and stop (via reset) animations. It would be good to be able to pause and restart animations. Something like this might work although it may be overkill.

A simpler solution might be to clear all callbacks on pause, then restart callbacks using the current date as a reference point. The date can be obtained from the date slider map overlay. This option would require modifying the animation functions to take the pivot time as an argument and potentially caching the filtered data, since we would not want to be fetching nor geographically filtering the data upon each unpause.