- Fix indenting.
- Small wording fixes.

- Add ADR describing Plugin Contexts
- Remove app-specific constants from framework-level code
- Add dashboard constants to student app with README

[TNL-7051] Clicking a video XBlock's fullscreen button now takes the video fullscreen instead of full window.

Gracefully fallback to full window if fullscreen apis are absent

This will remove imports from __future__ that are no longer needed.

https://docs.python.org/3.5/library/2to3.html#2to3fixer-future

now that we install it from an external repository.

Refactored the previous best-practices document as an ADR.
Previous document: https://github.com/edx/edx-platform/blob/07f588517b11dea238aadff80c9daf3b36e1a3aa/docs/best_practices.rst

This is part of a larger effort to split packages out into independent,
composable, PyPI installable Python packages.

While this package itself isn't monumental, it represents the bottom of
the dependecy tree and can be split out before any other packages.

This basically commits the transpiled CoffeeScript JS (with minor
cleanup) and removes coffee build support.

A tiny amount of support for xblocks exists, because external users
may have xblocks with coffee. But no coffee in our tree anyway.