Overflow form input labels to new line.

Push input boxes to last line of label.
Fix for helptext overlap on input boxes.
Flow helptext to right of input boxes on forms.
Make flow of form elements vertical rather than 'table-like'.
Fix to prevent barrage of errors on cancel event.

Also - prevent continuation of download after cancel event on refresh.
Removed fixed width from form label.
Create separate exception catch for DownloadCancelled in video download Command.
Stop prevents launch of cron in force_job
Merge pull request #1532 from rtibbles/cancel_video_download

Fix to prevent barrage of errors on cancel event
Merge pull request #1471 from rtibbles/user_signup_overflow

Make text on all input forms to overflow properly
Moving shared/caching to main/caching
Merge branch 'develop' of github.com:learningequality/ka-lite into eliminate-shared

Conflicts:
	kalite/shared/jobs.py