Milestone M33 - embed fix, timeout fix and more

Let's go through what we got done in Milestone M33 (Mar 24 - Apr 06).

Bug fixes:

• The /progresses client side API endpoint for courses was giving timeouts every now and then. We made a conditional query optimization in result generation when students are logged in and fixed it.

• NeetoQuiz embeds were not working as page component blocks on newly created pages because of an issue with parsing that got introduced into the system when we moved to block based UI. We fixed this issue.

• Since adding a bunch of missing foreign keys to fix active_record_doctor issues from M32, a few issues sprung up where the cascaded destroys started failing when trying to incinerate/destroy some of the resources. We manually added an on cascade: delete for such foreign key relations.

• A few other minor issues came up because of added foreign keys, that required specific exception handling in places where duplicates records creation was not considered earlier. These instances were fixed.