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.
Instead of adding the event listener in js, you can do `on-analytics-query-change={{queryUpdated}}` on the polymer-element. Then define `queryUpdated`. If you don't want that method on your element, what you have is also fine.