Implement next generation modulestore

A new modulestore backed by mongo that changes the data format to
facilitate easy versioning, sharing content between courses, and fast
lookup of course structure and Scope.settings data.

Conflicts:
	cms/djangoapps/contentstore/tests/test_contentstore.py
Make tests not msec time sensitive
Ensure kvs up-to-date if code accessing it.
Move default set_many impl to xblock
PEP8 and Pylint fixes
Merge pull request #271 from edx/dhm/next-gen-modulestore

Next gen modulestore