Cache ml grading pending in order to avoid repeated expensive function calls.
Address review comments
Fix keyerror
Add in some constraints to tables
Rename cache keys
Add in a management command to clean duplicates (good to use prior to deploying)
Rename everything
Merge pull request #133 from edx/fix/vik/high-ora-cpu

Reduce ORA cpu usage by caching some expensive queries
Try to control growth of duplicate grader sets
Address review comments
Fix unicode rubric problems.
Fix tests by making unique xqueue ids
Actually fix tests
Merge pull request #136 from antoviaque/master

config-prefix: Allow to specify SERVICE_VARIANT, used as config prefix
Merge pull request #134 from edx/fix/vik/calibration-500

Fix/vik/calibration 500
Merge remote-tracking branch 'origin/master' into fix/vik/bad-duplication

Conflicts:
	controller/models.py
Fix loop logic
Add in error templates
Merge pull request #135 from edx/fix/vik/bad-duplication

Try to control growth of duplicate grader sets
Merge pull request #137 from edx/fix/vik/error-templates

Add in error templates