Use sass for stylesheets

Use the maven-sass-plugin to compile our scss files into css

https://www.pivotaltracker.com/story/show/69670956
Use color variables in the sass

https://www.pivotaltracker.com/story/show/69670956
Add box-shadow to access revocation modal.

https://www.pivotaltracker.com/story/show/69670956
Use variables to dry up header and footer spacing

https://www.pivotaltracker.com/story/show/69670956
DRY up CSS with SASS nesting.

https://www.pivotaltracker.com/story/show/69670956
Extract font weights into SASS variables.

https://www.pivotaltracker.com/story/show/69670956
Update README to include SASS.

https://www.pivotaltracker.com/story/show/69670956
Merge branch 'feature/sass' into develop