Added new functions, colors, and variables

- Included list functions from compass (no-bullets and pretty-bullets)
-Added cross-browser opacity mixin.
-Added compass-esque contrast checker (set-text-color) to make sure
text is legible with a background-color.
-Added class-based headings to typography (allows the inclusion of .h1,
.h2, etc.)
-Changed brand colors to $primary-color and $accent-color
-Added app.scss for app-specific styling.