Add Sass Grunt task

* The Sass Grunt task can be run with "grunt sass:dist" or the Sass source can be watched/built continuously with "grunt dev"
* The "grunt default" task now runs the Sass build task and the new karma unit test task.
* "npm test" now runs "grunt default" (build Sass -> run unit tests)
* Also, added a top level jshint task that can be run with "grunt lint"
Merge pull request #67 from ethanhann/feature_build_sass_themes

Add Sass Grunt task