Add ability to handle collections
Cleaning up the relationship between Moodle status and Mahara status

The Moodle submission has two independent status parameters:
1. Its "lock" flag can be LOCKED or UNLOCKED
2. Its submission status can be:
 - DRAFT: This is the status they start in if you require students to
  hit "submit"
 - SUBMITTED: The status after the student submits it, or after they save
  if you make the "submit" button not required
 - REOPENED: If you turn on multiple attempts, then each time you grant a
  new attempt it creates a new submission in this status.

The Mahara view can either be locked (i.e. submitted) or not

The Mahara view should be locked if and only if the Moodle submission
has the LOCKED flag AND/OR the SUBMITTED status. Any time we change
one of these parameters, we need to check the other one before we change
the Mahara view's status.
The lock() method was sending the admin's username instead of the student's
Adding missing lang strings
Update the message for viewing previous attempts
Add a setting to let the Mahara submission be ticked by default
Unsubmit the Mahara page/collection if the assignment is reopened

Requires this core patch: https://tracker.moodle.org/browse/MDL-44971
Fix the display when there are pages & collections, but none that you're allowed to submit