TIM-337: Feedback on assessment UI

[TIM-337](https://edx-wiki.atlassian.net/browse/TIM-337)

Design changes:
* provides static states for submission cases
* adds in abstracted system-feedback sass partial
* adds in starter animation sass partial
* syncs up loading style for steps with standards
* moves message UI archetypes/variables to the xblock level of Sass architecture

Dev changes:
* Move JS grade step into a separate file
* Feedback on submission UI wiring

Other goodies:
* Added a script for compiling sass to css

@talbs I squashed your work in #207 into this commit.  Could you take a look and make sure I didn't mess up the rebase?

@stephensanchez