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.
Commented code.

Also:

```
from .utils import render_template, AttrDict, load_resource
```

The utils have been factored out to the xblockutils repo, to avoid repeating many copies over all the XBlocks. The only thing to keep in mind is that it requires to include the xblockutils repo as a second requirement besides the xblock itself in the LMS.