Periodically autosave answers on timed gateway tests

[xcompass]

Periodically submit the gwquiz form in the background as a preview request on timed gateway tests, so the server saves the student's latest answers and work is not lost to a crash or dropped connection.

Per review: disabled by default. Set $gatewayAutosaveInterval (seconds) in the course environment to enable and control the period. Saves are skipped when answers have not changed since the last save, and the interval is randomized upward by up to a third to stagger load. Not active when an instructor acts as another user.

No server code changes; the preview pipeline already stores last answers.

[drgrice1]

This is not the right way to do this. Submitting a test already causes a lot of server overhead, and so making a test preview auto submit on a regular basis is really not going to work. Particularly with no option to disable it, and no options to set the period or anything.

This will need more thought and better development. In any case, this is certainly something that will need to wait until the next release. Please re-target to the develop branch.

[xcompass]

Changed target to develop. Happy to discuss it further. I'll add an option and have it disabled by default.

[xcompass]

Added the option: $gatewayAutosaveInterval in defaults.config, in seconds, 0/off by default — nothing renders and no timer is started unless a site or course sets it. The period is fully configurable through it, and saves only happen when answers actually changed. Also rebased onto develop as requested.

[dlglin]

There have been many discussions about how to improve the capture of student answers if they don't submit the exam (including #1156).

At this point having one question per page has almost entirely solved the issue for me since answers are saved when a student navigates between pages. Historically this caused other problems because students would submit the entire exam after answering the first question, but there are now multiple features that have reduced that to a very rare occurrence; namely the popup that appears warning students of this, and in the 2.21 release the "previous page/next page" buttons that are more prominent than the "Grade Test" button.

Here are a couple of alternative ideas for saving answers:

1. Have a "save answer(s)" button next to each question. The easy way to implement this would be to just have this button trigger an answer preview since that saves the student's answers.
2. Set up a javascript trigger that saves an answer as soon as a student navigates out of an answer blank. This would be complicated to implement since there are things like multianswer to account for, and it leads to similar load issues to what @drgrice1 described. I'm also not convinced that it would provide much more benefit than one question per page.