(WIP) Visual styling changes to basic LMS navigation, still under early review

This was the outcome of a quick bit of visual style tinkering, and it will require a great deal more of review, testing, and discussion before it can be considered as a platform PR. 

The following .gif shows the visual changes proposed. 
https://s3.amazonaws.com/uploads.hipchat.com/26537/183095/pBx50njoZgW2qRV/concept-styling.gif

In short, the idea is to visually reduce weight and grey noise in the main LMS navigational experience, along with eliminating grays and gradients where they aren't adding navigational clarity.

I've left all of the tinkering commits intact, allowing anybody to play around or comment on any of the various approaches tried along the way.