various UI enhancements

 *  new look
 *  file load/save support
     *  remote or local storage
 *  bookmarkable urls
 *  light/dark themes
 *  help dialog
 *  added grunt build for front-end (see CONTRIBUTING.md for details)
 *  moved docs to README.md

![image](https://f.cloud.github.com/assets/253069/2215313/3d1ccf38-99ed-11e3-8c55-2011b2eb6ced.png)