T37 show associated collections

I opted to break this into smaller steps:  first implement in our local, gw-sufia repo - that's this pull request.  But as soon as possible, we should submit this as a pull request to projecthydra/sufia - the primary reason is that we are overriding two files:
- app/views/generic_files/show.html.erb
- spec/views/generic_file/show.html.erb_spec.rb
As soon as either of these files change in projecthydra/sufia, we are susceptible to problems using newer versions of the sufia gem, and/or the need to continually merge those changes into our local overrides.

Two things need to happen before we can submit to sufia:
- Obtain GW OGC-signed CLA
- Add one missing spec test - see "#TODO" in spec/views/generic_file/show.html.erb_spec.rb .  I have been having some trouble writing this spec test at the moment so opted to separate this out into a (to-be-created) new ticket.