Keep playing .webms in clones.
Wait for the video metadata to be loaded before completing the expansion.
Don't add the 'expanding' class when unecessary.
Pause videos when they are not visible. #1538
Automatically play/pause videos in clones too.
Fix EAI loading files in hidden posts. Fix #1542
Changelog.
After contracting, isExpanding should be falsy.
Refactor ImageExpand.waitExpand():

- wait for the first frame to be loaded instead of the metadata before expanding.
- to my understanding, browsers will not always start the download immediately
  if the video isn't on autoplay, force it with load().