Move mimetype addition to common initialization.

Anonymous users may now view units in the courseware. This access is limited to units that are not considered problems/graded (e.g. homework, exams).

- Remove usage of django.urls.patterns
- Change urls tuples to lists
- Make all string view names callables

- Enables a method of deriving Django settings from other Django
  settings after all other Django settings are stable.

django.util.unittest was deprecated in django 1.7 and removed in 1.9.

PLAT-1551

LEARNER-2307

In particular, implement a validation API for registration,
where a client makes AJAX calls to the endpoints requesting
validation decisions on each input. Responses are strings
dependent on the type of validation error; if no error,
then empty string to indicate OK.

with a custom patch needed by edx-platform.
Upgrade django-filter as well to v1.0.4
Import DjangoFilterBackend from the correct module - django_filter.
Add django-filter to INSTALLED_APPS.

It accounts for a large chunk of our splunk logs and is often
repetitive.  See forums connections which on a sandbox do:

```
Starting new HTTP connection (1): localhost
```
and
```
comment_client_request_log: request_id=06ac65d3-61b9-4882-9edb-c6b65709318a, method=get, url=http://localhost:18080/api/v1/users/5, duration=0.0101051330566
```

Add this for any other IDA call.

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

In production environments, the DiscussionXBlock was generating CSS and
JS asset URLs that pointed to the unminified versions of those bundled
assets. Due to our nginx rules, this would cause the assets to be
served without the long expiration times, forcing the user's browser to
constantly refetch these assets while browsing a course.

[PERF-431]

Learner-1111

The internal_api_url field has been deprecated. All usages have been updated with calls to the method get_internal_api_url().

LEARNER-1111

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

Also add it to the course home page.

Although we are phasing out our support of OIDC, this particular feature will allow us to eliminate many of the settings we
share across services. Instead of reading various endpoints and secret keys from settings or hardcoded values, services
with the proper authentication backend can simply read (and cache) the information from this endpoint.

ECOM-3629

Some result sets may be larger than the default cache's 1 MB max item size. This change is a bandaid meant to allow us to resume use of memcached while we work on a longer-term fix.

LEARNER-682

This change brings the Credentials API calls in line with those of other services. The change also makes it easier for the future switch to an asymmetric signing key.

LEARNER-629

This information mirrors the fields returned in our ID token for OpenID
Connect (OIDC). Including this information will allow us to eventually
migrate toward replacing OIDC with OAuth 2.0 + JWT.

ECOM-3628

TNL-6689

for TNL-6644

TNL-6518