Peer Grading Interface

for code review issues

Add property to course module to check if a course is new

The property can be set in the policy metadata. If it is not specified
then it is set to true if the course has not started yet.

Also adds a property to check how many days are left until the course starts.

Feature/ichuang/update symmath server

Merge pull request #1227 from MITx/feature/ichuang/fix-capa-contextualize-text-for-option-response-and-mc

fix capa to add contextualize_text for optionresponse and multiplechoice

Fix parent lookups when the same named tag exists in multiple courses

The parent trees are built on a per-course basis (so it'll throw ItemNotFoundError
if an item exists in a different course from the one you're asking after. NoPathToItem
can still happen with MongoDB backed courseware. They store things like the info page
as HTML snippets which are orphaned from other content.