Made submitter required.
Merge pull request #186 from Cal-CS-61A-Staff/submission_check

Add submission checks and anon user key.
Made anonymous users have a key.
Made anon users not be allowed to index submissions.
Merge remote-tracking branch 'origin/master' into submission_check
Merge pull request #187 from Cal-CS-61A-Staff/submission_check

Submission check.
Merge branch 'master' into groups
Fix anon user get_or_insert.
Merge branch 'master' into groups
Merge branch 'groups' of github.com:Cal-CS-61A-Staff/ok into groups