various UI enhancements

 *  UI improvements
 *  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/253069/2215367/03ff65ec-99ef-11e3-93ea-10ed0e3b5a68.png)