New drawing app. for drawing interaction: add text tool, remove spray
brush, allow multiple interactions on the same question (runtime only),
based on frabric.js

It's prevent setting the transaction in error status if the revision is
missing

Allow batch deletions of several users at once, use assessment entries
to reduce the number of courses to scan, don't load courses, but only
structures (DB free)...

Add a retry to selenium tests as to biggest source of failed test is
browsers which doesn't want to start