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?
Integration tests use consistent teardown methods
Caching db config in migration utils
Fix tests tripping spam protection
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
Pagination for Users Management screen

closes #3222
- implementing server-side pagination for /users API
- passing /users?limit=none will return all users
- passing /users?status=invited will filter base on user status
- creating 3 mixins (route, controller and view) to keep pagination logic DRY
- updating route, controller and view for Posts to use new mixing
- implementing infinite scrolling for Users Management screen (using new mixins)
- Users Management screen displays all invited users, but paginates active users