[LMS-2757]

Fix acceptance and unit tests

LMS-1296

This commit adds the non-courseware lms/djangoapps and lms/lib.

These keys are now objects with a limited interface, and the particular
internal representation is managed by the data storage layer (the
modulestore).

For the LMS, there should be no outward-facing changes to the system.
The keys are, for now, a change to internal representation only. For
Studio, the new serialized form of the keys is used in urls, to allow
for further migration in the future.

Co-Author: Andy Armstrong <andya@edx.org>
Co-Author: Christina Roberts <christina@edx.org>
Co-Author: David Baumgold <db@edx.org>
Co-Author: Diana Huang <dkh@edx.org>
Co-Author: Don Mitchell <dmitchell@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Nimisha Asthagiri <nasthagiri@edx.org>
Co-Author: Sarina Canelake <sarina@edx.org>

[LMS-2370]

LMS-2565

Add cache-based locking to subtasks to ensure that the same task is not running in two workers at the same time.

Add cache-based locking to subtasks to ensure that the same task is not running in two workers at the same time.

Adds the edX Marketing-approved template as html default.

Includes Data + Schema migrations for optout email -> user.id change.
Note that migrations should be reversible.

Some minor pep8 cleanup