VE-1613: Support for MediaGallery paremeter - expand - in VE

Changes seem pretty significant and this is because it's not only support for displaying but also for changing value of expand. So if you process transaction similar to this: ve.dm.Transaction.newFromAttributeChanges(ve.instances[0].view.model.documentModel, 8, {expand:false} you will notice that diff looks correct.

https://wikia-inc.atlassian.net/browse/VE-1613
VE-1613: Small optmization to variable initalization and assignment
VE-1613: Fixed typo
VE-1613: Proper handling for expand in new galleries
VE-1613: Improved handling for "expand" property - modify it only when necessary (clean diffs)
VE-1613: Use correct quote marks
Merge pull request #5199 from Wikia/VE-1613

VE-1613: Support for MediaGallery paremeter - expand - in VE