Moved to google-apis, added JSDoc

Switched over to the google-apis element for loading in the YouTube
iframe API, and added a bunch of JSDoc comments.
Modifications from code review

Addresses some of the feedback from
https://github.com/jeffposnick/google-youtube/commit/fdc00121b1f0e18cca2
e23267e77474fb509e883
JSDoc tweaks

Primarily JSDoc tweaks, as well as explicit checks that this.player is
set before calling methods on it.
Changed the hardcoded video id in the JSDocs to “…”. Added an explicit
mention of the default video id value in the JSDocs since @default
isn’t picked up by the page generator.
Merge branch 'to-be-reviewed'
Added explicit dependency on Polymer/polymer#master