adds mobile, drupal, and request api

Closes #666 :scream: 

Helper methods ported over wholesale with a few modifications. All tests ported over and were most helpful. :+1: for tests
I'm beginning to think we should just kill the mobile availability for now.  The only known consumer (given that we explicitly exclude this for the drupal API) is the iStanford app, which has dropped support for the API in the first place.

If we wanted to re-add it in the future we would want to re-write most of it to use the new mechanism for looking up the availability of an item ( https://github.com/sul-dlss/SearchWorks/blob/master/lib/live_lookup.rb ).  I'm sure we could drop it now w/o consequence (and get rid of some of the legacy code in the same step).