Fix file validation for importer

refs #3339
- wrong call to file validation
- refs the issue because I get application/json on OSX? Is this
something Windows specific?
Add relationships to client models

No issue
- Removed tabs from tag.js (why didn't jshint catch this?)
- Removed superfluous `activate` in SettingsIndexRoute
- updated `UserModel` and `TagModel` to have `created_by, updated_by` be references to `user` objects.
- updated `UserModel` to use `moment-date` instead of `date`
Merge pull request #3340 from sebgie/issue#3339

Fix file validation for importer
Merge pull request #3345 from novaugust/model-relationships

Add relationships to client models
Refactor fixture use in tests

no issue

- Refactor all integration tests to specify and load ONLY the fixtures
  they require to run, rather than initialising the whole kit-and-kaboodle
  for every single test which takes FOREVER.
- Refactor the route tests to share a doAuth function, and also specify
  additional fixtures required
- Move import and export unit tests, which are actually integration tests
  (they touch the DB)
- Comment out most of the permissions unit tests for now as they need more
  stubs/mocks so as to not touch the DB

Still todo:

- prevent default DB initialisation in route tests, and specify all
  fixtures requires as per the integration tests
- fix up the unit/permissions_spec