Add google-analytics element files.

There are a few additional features I'd like to add, but I wanted to get the base stuff committed first.

In the future I think we can remove the dependency on the [Embed API](https://developers.google.com/analytics/devguides/reporting/embed/v1/) completely and just use `<google-chart>` and something like `<core-ajax>`, but for now this is working pretty well.
you should create an instance var in ready:

    ready: function() {
      this.query = {};
    }

so there's no shared state across multiple instances of google-analytics-dashboard on the page