adding Sass architecture:

* import order - with base blocks, theming, and specific app layers
* base utilities/tools
* notes/starters for each Sass partial imported

TIM-127
adding basic/problem-centric styling support and FED fixes:

* adding in missing Font Awesome font assets
* correcting path for Open Sans typeface
* correcting typo in notes of openassessment IE-specific Sass
* syncing up variable names/values
* adding additional wrapper--grid element into layouts for easier grid-based styling
* syncing up variable names/values
* initial grid/view-based styles
* initial typographical styles
revising markup and styling for oa_*.html templates:

* matches static template expected markup
* adds in missing classes
* revises indentation/nesting
* adds in system__element markup/styling for system-based DOM elements