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.

LEARNER-2736

  all dirs must now go into COMPREHENSIVE_THEME_DIRS.
Move comprehensive theming setup section out of startup.py and into
  settings files using new 'derived' functionality.
Add 'derive_settings' at the end of all top-level Django settings files.
Move validation of comprehensive theming settings into new apps.py
  theming file.
Split theming code into code safe to run before settings are initialized
  -and- after settings are initialized.

RSS_TIMEOUT was removed in e8ee2978
but missed in lms/envs

ANALYTICS_API_KEY was used to make direct requests to the
ANALYTICS_SERVER_URL which was our original original analytics effort.

We cleaned out the feature flag and code using these in
https://github.com/edx/edx-platform/pull/5707
but missed the config (I'll go get them in configuration.git later,
when I pull them out of the secure repos, which is where I found them).

EDUCATOR-565 | Add POLICY_CHANGE_GRADES_ROUTING_KEY, fix errors in compute_all_grades_for_course circuitry.

PSA was monolothic, now split, with new features, like
a DB-backed partial pipeline. FB OAuth2 version also upped.

Partial pipelines don't get cleared except when necessary.
They persist for special cases like change of browser while
still mid-pipeline (i.e. email validation step).

Refactor, cleanup, and update of a lot of small things as well.

PLEASE NOTE the new `social_auth_partial` table.

- Keeps platform set default of "Audit" to be backwards compatible and not break stuff
- get COURSE_MODE_DEFAULTS from config if set

move tasks into tasks.py

add more logging

Defaults to SUPPORT_SITE_LINK intentionally.
Also fixed surrounding quality tests, and overall
quality improvements.

This also serves as a slight refactor of ENT-392.

Pulling URLs from settings allows us to rely on site configuration overrides in order to support multi-tenancy.

LEARNER-1103

Add Enterprise sidebar to login and registration views; remove unneeded fields; make registration form more narrow