adding transition state for form inputs' placeholder UI
making step__status elements' visual width equal in all cases
cleaning up step__title and step__status UI for responsive layouts
adding visual emphasis to problem's prompt UI
adding graded + required UI back into step__status for peer assessment templates
adding collapse/expand toggle to assessment feedback form UI
aligning step__status icons/text to be left-justified
revising introductory message copy
adding visual spacing between grade report UI sections
finalizing assessment feedback UI
syncing up step__status positioning for larger desktops
Merge pull request #214 from edx/talbs/ui-cleanup

UI Clean Up - Small Tweaks
Course staff can see counts.
Add UI styling for course staff, including collapse/expand.
Cache student item when retrieving submission and student item.
Protect against invalid cache key exceptions.
Update test suite to clear cache between tests.
Add composite index for AssessmentWorkflow student item fields