The existing pattern of using `override_settings(MODULESTORE=...)` prevented
us from having more than one layer of subclassing in modulestore tests.

In a structure like:

    @override_settings(MODULESTORE=store_a)
    class BaseTestCase(ModuleStoreTestCase):
        def setUp(self):
            # use store

    @override_settings(MODULESTORE=store_b)
    class ChildTestCase(BaseTestCase):
        def setUp(self):
            # use store

In this case, the store actions performed in `BaseTestCase` on behalf of
`ChildTestCase` would still use `store_a`, even though the `ChildTestCase`
had specified to use `store_b`. This is because the `override_settings`
decorator would be the innermost wrapper around the `BaseTestCase.setUp` method,
no matter what `ChildTestCase` does.

To remedy this, we move the call to `override_settings` into the
`ModuleStoreTestCase.setUp` method, and use a cleanup to remove the override.
Subclasses can just defined the `MODULESTORE` class attribute to specify which
modulestore to use _for the entire `setUp` chain_.

[PLAT-419]

ECOM-891: Allow tracking of invoice transactions.

Authors: Awais Qureshi and Aamir Khan

- Price field added to Advanced Settings
- Function that decides which price to display
- Test added to check that the function outputs correct price
- Added feature flag and conditional to decide whether to display course price or not
- Feature Flag to show or hide course price on Course About page sidebar when not using shopping cart

TNL-1304

Move default country access messages out of static_templates, so they are not served by other Django views.

These were found by the new pylint checker I wrote! :)

Add Django admin UI for configuring country access

Migrate existing embargo rules into the new tables.

PLAT-420

Bok choy will now be broken as follows:
* shard 1
* shard 2
* shard 3
* default shard (i.e. 'none of the above')

We use our shards to break up work and reduce overall test time by leveraging
multiple test systems.

Makes logistration available at /login and /register as well as /accounts/login/ and /accounts/register/. In addition:

- Adds support for redirect URLs in third party auth for combined login/registration page
- Adds support for external auth on the combined login/registration page
- Removes old login and registration acceptance tests
- Adds deprecation warnings to old login and register views
- Moves third party auth util to student_account
- Adds exception for microsites (theming)

Conflicts:
	common/lib/xmodule/xmodule/css/sequence/display.scss

ECOM-963

update copy in tests

Removes old payment and verification endpoints, views, templates, and tests, making the new split flow the default. The SEPARATE_VERIFICATION_FROM_PAYMENT feature flag is also removed.

ECOM-1007

TNL-1185

TNL-1185

This reverts commit 66b949b7.