* Add verification deadline model.
* Populate verification deadlines from course modes table.
* Update student dashboard to use verification deadlines.
* Update pay-and-verify view to use verification deadlines.
* Simplify Django admin for course modes and add validation.
* Add verification deadline to Django admin for course modes.
* Add UI for when the upgrade deadline is missed in the pay-and-verify flow.

Add context for navigation states
added find course to dashboard sidebar and included check for context that Will adds in PR
removed nav_course_search context due to design change so replaced with nav_hidden
Removed rwd_header.js and all references as no longer being used.

Wrapped Find Courses in dashboard sidebar in if statement

* Adds a credit course mode to indicate that a course
has a credit option.

* Hides the credit option from the track selection and
pay-and-verify pages.

* Shows different messaging for the verified track if
it's possible to upgrade from verified to credit at the end
of the course.

XCOM-94

The new "country access" implementation replaces the old
implementation.  Middleware and tests have been updated
accordingly, but deprecated models are preserved
for backwards compatibility.

Block users from enrolling in a course if the user
is blocked by country access rules.

1) Enrollment via the login/registration page.
2) Enrollment from the marketing iframe (via student.views.change_enrollment)
3) Enrollment using 100% redeem codes.
4) Enrollment via upgrade.

This does NOT cover enrollment through third party authentication,
which is sufficiently complex to deserve its own commit.

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]

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.

Adds mode creation endpoint to course_modes app and ability to bypass media device access prompt when proceeding through verification flow in a testing environment.

Set marketing site logged in cookie from third party auth.

Update devstack settings to use new CyberSource API

Add session middleware to an external auth test to fix a test failure with the auto-registration AB-test changes

- Changes registraiton button text for professional ed courses
- Professional ed courses do not see "choose your track" page; go straight to verification flow

- Changes registraiton button text for professional ed courses
- Professional ed courses do not see "choose your track" page; go straight to verification flow

Fixes LMS-2830