adding transition, error and complete states for assessment feedback form:

* 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

Move JS grade step into a separate file
Feedback on submission UI wiring
Generate JavaScript fixtures from Django templates
Merge pull request #218 from edx/will/assessmentfeedback-submit

TIM-337: Feedback on assessment UI