Reveal full text when metadata panel is opened

Automatically reveal/hide full text as metadata panel is opened/closed.
Also makes metadata open/close a proper event.
Changes scrollTop calculation for the fully open metadatapanel so it is not
confused by the size of the panel changing.

Also rename MetadataPanel.$controlBar to $aboveFold (that field was missed
when the corresponding CSS class got renamed).

Change-Id: I7e66ca0f45c2188dab4b78508ad7f91154187de4
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/396
Merge "Reveal full text when metadata panel is opened"