STUD-600

Adding to installed Django applications is required due to the use
of a Django model by the XBlock

http://bgrins.github.io/codemirror-accessible/)
LMS-1802

Finalize tests for embargo middleware app

Adds configurable middleware in common/djangoapps/embargo that
allows specific courses to comply with US Export regulations by
embargoing students from specific countries, whilst simultaneously
allowing other courses to be freely open to all.

add new feature to make sure we aren't writing PII into the application logs. So far we're aware of doing so regarding Auth use-cases

UX-381

Caution! This is backwards incompatible

Also, refactored code representing ReverifyInfo

Added verification sidebar, banner for major courseware sections, quality & test improvements

Add optional feature to lock out accounts after N failed login attempts. Lockouts will last M seconds.

add DB migration and fix earlier mistakes in student migration history

add tests and fix bugs that came out of those unit tests

remove unused import

pep8/pylint

address some PR feedback

fix tests

fix broken test

try to mock time

use freeze-gun to overload the system time to simulate the future

ConfigurationModels can be managed using the admin site. They are
append-only, and track the user who is making the change, and the time
that the change was made. The configuration is stored in the database,
and cached for performance.

[LMS-1220]

To mark a language as dark-launched, add it to the DARK_LANGUAGES
django conf setting. To activate a dark-launched language, set he
query parameter `preview-lang` to the language code on any url.

[LMS-2045]
[LMS-2077]
[LMS-2076]