Update to Ed's dev branch of RestPack

Closes #311
Use proper links for user projects

Closes #320
Use Polymorphic support to simplify VersionSerializer
Update to bugfix version of restpack
Make SubjectSet to Workflow relationship 1 -> *

Remove HABTM relationship between SubjectSet and Workflow so a workflow has
many subject sets and a subject set belongs to a single workflow. This will
support being able to set retirement rules on subject sets.

Closes #148. Closes #338
Merge pull request #351 from edpaget/use-dev-restpack

Use dev restpack
Merge pull request #354 from edpaget/has_one_subject_set

Make SubjectSet to Workflow relationship 1 -> *
Allow searching of groups by name