Merge Invites branch and resolve conflicts

* Batch invites
* CSV invites import
* More controls on the students invites
  * Force resend invite
  * Send pending invites only
* Add sent field to StudentInvite

* Authorization for students to fill form
* Fix typeahead for new elements
* Few minor view fixes to support student authorization
* Invite codes are now reset once the form is filled

Fix send JSON for recipient vars