TNL-1336

ECOM-891: Allow tracking of invoice transactions.

Authors: Awais Qureshi and Aamir Khan

Fix link stylings in LMS and CMS footers

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)

ECOM-1002 fixed issue of grey background for logistration page. Also fixed focus issue when toggling between forms - as raised by @cptvitamin

This reverts commit b8184d18.

[second attempt which addresses bug building Studio]

This reverts commit 1d6fceda.

UX-1466

Respond to review comments:

- Rename build and config files for consistency between lms/studio.
- Fix merge conflicts with lms require config.
- Devstack uses optimized pipeline to skip require JS optimizer step
- Add tests for render_require_js_path_overrides

Several IE bugs have been fixed in 2.4.

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.

TNL-1137

TNL-653