Add timeline.running property
Add timeline.running property

Add a new “running” property as a companion to “undoing”, that is
true whenever (forward or backward) timeline actions are being
executed.

This will eliminate the need for tricks like the triggered_move
flag in https://github.com/robinhouston/talkie-leaflet/commit/7b83f10d3bab174e7d83df3bbdafe645e7eeed82

kiln/talkie,kiln/talkie,kiln/talkie