[DO NOT MERGE] Add proxy deposit and transfer of ownership

**DO NOT MERGE** This branch is a WIP, with 12 feature specs still failing. It pulls in a few related features from ScholarSphere including proxy (on-behalf-of) deposit, "sticky" proxies, and transfers of ownership, all of which revolve around the idea of one user depositing files on behalf of another.

I'm looking for:

1. Someone to do a preliminary review of this code so I can make any major corrections before submitting the mergeable PR later this week.
2. A kind soul who may be able to take a quick look at the failing specs and give me a second set of eyes re: the 12 spec failures. The specs that are failing are spec/features/{collection,proxy,ownership_transfer}_spec.rb and my best guess about the failures is that they're related to the select2-rails gem.

Anyone up for lend a helping hand?  I'd be much obliged for either.  Check out Travis to see the failures.