Fix problems with size menus for embed and download

I think this takes care of all the different mutations of
weird states that happen when going from a small to large
images and transitions in the middle, see card/386.

Change-Id: I80527d746614c0bbda7a1084061d292e5d6394a8
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/386