Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

DraftModuleStore was originally designed as a mixin, but never used that
way, and with the upcoming changes to use the versioned module store,
never will be. This changes removes a circular dependency between
mongo.py and draft.py.

Moved xml_store_config, mongo_store_config, and draft_mongo_store_config to xmodule/modulestore/tests/django_util.py
Removed some repeated instances of xml_store_config.
Reverted some changes to mongo_store_config so each modulestore gets it's own uuid.

Conflicts:
	lms/djangoapps/courseware/tests/test_navigation.py
	lms/djangoapps/courseware/tests/test_view_authentication.py
	lms/djangoapps/courseware/tests/tests.py

Make django use_tz

fix broken tests. Also drive by fix for the sporadic failure on tests which may go to a textbook page. The URL formatting was incorrect in the test

Now that we are using separate pages for login and registration rather than
modals, clicking the registration button for a course should direct an
unauthenticated user to the registration page, and the user should be enrolled
in the course upon successful registration. Likewise, an unauthenticated user
attempting to unenroll from a course should be directed to the login page and
subsequently unenrolled from the course upon successful login. The enrollment
change service also now uses HTTP status codes rather than JSON to communicate
status to the front end.

pylint

add fixes for 500 bugs (lighthouse 287 and 293) by requiring login for accessing licenses and inline discussions.  Add unit tests for licenses, and rearrange tests based off of (the former) PageLoad.  Also cleanups for pylint and pep8.