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.
In the future, you may want to consider using `<content select="google-analytics-chart">` to only bring in chart elements to the dashboard. Insertion points are a rendering thing though. I realize you have other elements that are children of google-analytics-dashboard that don't render things.