[Vault]: Load preview for version 0 of a question

... given that we are now generating all 4 version previews for each
question in the vault
[preview]: Pick a random version from the vault/

Not only will this bring variety in every session, it will also
be a test that all versions for a question have been created
properly
[preview]: Temporarily reverting to old behaviour ...

Cron-job issue on Linode w/ new build structure is still unresolved.
That needs to be fixed first
Student registration
- moved to outside the site
- registration now results in student *claiming* their account which was already created
Merge branch 'newstudentreg'
Merge remote-tracking branch 'upstream/master'