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.
Is there a convention we have for exposing component state for CSS styling? I wasn't sure if I should use an attribute, a data-attribute, a class, etc. A attribute seemed to make sense to me, but I'll do whatever the convention is.