Update kept to work with the new daybed.js

This uses the new daybed.js API and works with kept to share the dashboards, using a hash in the url.
With promises you can return either values or other promises. In this case, we could do something like this: 

```javascript

   var self = this;
   return Daybed.startSession(self._options.host, {
      token: this._options.token
   })
   .then(function(session) {
      self._session = session;
      self._prefix = PREFIX + session.token.slice(0, 5);
      self._options.onSession(session);
      return session.getModels();
   })
   .then(function (models) {
      // Make sure all needed models are defined.
      var modelIds = [];
       ...
   })

```