Introduce LMS_INTERNAL_ROOT_URL.

The LMS and edx-enterprise currently communicate via REST APIs, even
though they are all running within the same service.

Currently API URLs are constructed using LMS_ROOT_URL, but that is
problematic on some systems where the external LMS_ROOT_URL is not
accessible from the private network, or routing internal requests via
the external URL is not desireable.

This patch introduces a new setting variable LMS_INTERNAL_ROOT_URL which
defaults to the value of LMS_ROOT_URL for backwards compatibility.

The LMS and edx-enterprise will use LMS_INTERNAL_ROOT_URL to construct
API URLs instead of LMS_ROOT_URL.

Pin sorl-thumbnail to 12.3

Fix linting errors from https://github.com/edx/edx-platform/pull/16615

Merge release back to master

Fix a number of unused-import pylint violations

Change template's deprecated '=' comparison to '=='.

Better handling of data for OData API exception handling

Cale/schedules admin improvements

Fix Django 1.11 startup

New management command for setting up a test environment. The command creates a ScheduleConfig and schedules if they don't exist (the schedule starts three days before the time the command is run). If a schedule already exists, the command updates the schedule's start time and upgrade deadline. The values set by the command will allow send_recurring_nudge to send three-day nudges.

No unicode in "from" value on Bulk Emails

Remove uneccessary aria labels in the student dashboard

PLAT-1199 Stop using pycrypto

Until https://github.com/django-ses/django-ses/issues/137 is resolved, we need
to proactively search for and prevent unicode values in from_addr.

EDUCATOR-1773

PLAT-1413 Remove TEMPLATE_DEBUG setting

update edx-organizations version

Discussion Add Post - Add Explicit Labeling of Discussion Checkboxes

Discussion Add Post - Update sr Label to Match Visual Label

Avoid a django breaking change: set_language response code

In Django 1.10+, the set_language view (/i18n/setlang) will respond to
Ajax requests which do not contain a "next" parameter with status 204 No
Content instead of 304.  This commit adds the "next" parameter to the
request in order to ensure that upgrading to Django 1.10+ will not cause
the set_language view to change behavior.

PLAT-1353

Lower thresholds.