Support for displaying submissions API scores in Progress page.

All YouTube urls are defined on backend side.

Changed "Status Page" -> "Page".

UX:
    support for displaying built-in tabs
    restored drag and drop on Studio Pages
    additional styling for fixed state on Studio Pages
    add a new page action added to bottom of Studio Pages

Dev
    changes for viewing tabs in studio,
    refactored the tab code,
    decoupled the code from django layer.
    is_hideable flag on tabs
    get_discussion method is needed to continue to support
external_discussion links for now since used by 6.00x course.
    override the __eq__ operator to support comparing with
dict-type tabs.

Test
    moved test code to common,
    added acceptance test for built-in pages
    added additional unit tests for tabs.
    changed test_split_modulestore test to support serializing objects
that are fields in a Course.

Env:
    updated environment configuration settings so they are
    consistent for both cms and lms.

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