Add color monster theme

This PR (and its single commit) contains everything that is necessary to add a new theme (and nothing else)

There is a video demo here: http://screencast.com/t/ezDriv4P97Rx

  * Adds `app/themes/<theme-name>.js`, the file that defines the theme's structure
  * Adds `templates/themes/<theme-name>/<section-name>.hbs`, one template file for each of the theme's sections that can be added by a user
    * this theme adds `color-boxes.hbs` and `hero.hbs` because those are the two sections it uses, as defined in the `app/themes/color-monster.js` file
  *  Adds `templates/themes/<theme-name>/styles.hbs`, the file that is used to define specific styles for this theme, and shows the use of the `{{css-color}}` helper in it to show how to use dynamic/derivative styles based on theme variables
  * Updates app/themes/index.js` to add this theme to the list of possible themes

See in-line comments below for more detail.
the changes to the editor's hardcoded response from its `model` hook are just a convenience. This allows us to repeatedly reload the `/editor/undefined` url and have its page information reloaded each time. This just makes it easier to keep tweaking the handlebars and style information for this theme page. After the tweaking of the theme page stuff is done, the `sections` property of this object should get copied to the appropriate place in `app/themes/<theme-name>.js`