First stab at extracting a color palette

- Pulled out the existing palette in _mixins
- Took a stab at naming greys after their usage count in contexts
- Replaced #a40802 with #a80000, since they are very close and $red was already in the palette

Missed importing 'colors' in a couple of places

Removing a redefined  in favor of  in colors.css.scss

Fixing missed imports #2

Renamed $background to $background-white

Explicitly calling out the color of the background, since we have many
background colors
Merge branch 'ssrihari-color-palette' into develop