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.
[PERF-303] Integer XBlocks/XModules into the static asset pipeline.
This PR, based on hackathon work from Christina/Andy, implements a way to discover all installed XBlocks and XModules and to enumerate their public assets, then pulling them in during the collectstatic phase and hashing them. In turn, the methods for generating URLs to resources will then returned the hashed name for assets, allowing them to be served from nginx/CDNs, and cached heavily.
* when things don't load normally, use this
* separate raw editing functionality into EditingDescriptor
* raw descriptor just enforces that xml is valid
* add a MalformedDescriptor that just saves a string
* Fallback to it on import.
