Reduce roster lock conflicts by releasing locks on 'View Assignments'

[jefft]

Say we have users A and B:

• User A clicks 'Edit Assignments'
• User A immediately clicks 'View Assignments'
• User B clicks 'Edit Assignments'

User B will get a lock error:

The lock will persist for the "Lock Length" config setting number of minutes, and there is no obvious way for user A to 'unlock' the roster.

The problem is that while 'Edit Assignments' gets a lock, clicking 'View Assignments' does not release the locks. I believe it should: if you are on 'Edit Assignments', and click 'View Assignments', that is cancelling your edit. There is no other 'Cancel' button (unlike, say, recording attendance).

How about if, after clicking 'Edit Assignments', before making changes, the editor clicks the 'Home' button or any other app link? There is the same problem: they retain their edit lock. Unfortunately we cannot release the lock for them, because the situation is indistinguishable from them opening another tab, clicking around, and returning to their 'Edit Assignments' page. I have no solution for the general case. But the case of clicking 'View Assignments' on the 'Edit Assignments' page is special. We know that editing is over (unlike in the general case). Therefore we can release the locks.

[jefft]

PR #1108

[tbar0970]

Related: #583

[tbar0970]

Related #1063