[WIP] Implement Mobile Editor

- add FastClick library to Gruntfile.js
- add mobile-interactions and touch-editor to client/assets/lib/
- add mobile-specific tests to util/mobile-tests.js
- add util to setup mobile codemirror only if we're really on mobile
- change gh-codemirror from having a default action to a named action. prevents Ember.TextArea firing action on change
- change gh-codemirror `cm.getDoc().getValue()` to `cm.getValue()` for portability
- change codemirror-shortcuts ES6 export/import style

One thing that's definitely not working yet is clicking the "Preview" tab in portrait mode. Other than that I think most if not all of it is working.