[beta] Publish channel builds to bower.

Publishes builds to the main bower repo (https://github.com/components) after each Travis build on one of the channels.

A few details:
 * The builds are pushed to a branch on that repo for the given channel.
 * The version (in `bower.json`, `package.json`, etc) will be the same as the Ember.VERSION.
 * The commit message in the bower repo will point to the commit that it is referencing.