Refactoring: Use format with named variables

Adding a reviews page to the course and updating the reviews module on the course about page. Removed the existing coursetalk implementation and put it in a fragment, removed the tests as well. Added configuration settings to specify the reviews template as well as the reviews provider. This is all protected by a waffle flag.

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.

This feature is not always needed and is not properly provisioned for devstacks.

LEARNER-1341

- 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 reverts commit f97f0525, reversing
changes made to 800bcd8e.

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

This service is not currently available in Docker devstack.

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

The read_cached_programs switch was used to control the release of changes for reading programs exclusively from the cache. With those changes stable, the switch is no longer necessary.

LEARNER-382

* Reorders form fields, and updates labels, placeholders, and tip text
* Increases clickable area for links and labels.
* Removes "*" markers from required fields, and instead adds
  "(optional)" labels to visible optional fields.
* Updates font colors and sizes, and removes box shadows
* Adds custom drop-down styles
* Improves responsive design scaling for small screens
* Make Terms of Service and Honor Code open in new window to avoid losing form
  field values.

This makes it possible to refer to multiple book from a single app.

This also means that Open edX branches will be able to pass bok-choy
tests (at least if the books have already been built.)