Google Drive XBlock - Fake PR for review purposes, do not merge!

@martynjames Created this PR for the review. 

Btw for the future, it's easier to create this when the first commit is empty. Also, if we want to review a series of PRs at once instead of individual PRs, it would be easier to merge the individual PRs in a branch which isn't master, and then create a PR from that branch into master when it's ready -- this way we don't need "fake" PRs at all, they represent the actual review workflow.
This is a great idea for v2 - Depending upon the document type, the Google UI gives one the options and generates the embed code with your options. For MVP, Marco decided that he'd rather have the end user manipulate using the google UI, and then copy-paste the embed code directly from the google UI