Adding the ability to get realtime changes on files
for the purpose of push-notification/webhook style
watching and for folks to be able to implement sync
clients without trying too hard.

Work in progress:
* Need to ask some Google Drive platform folks what the various
Channel types are. I've currently found `web_hook` but that
requires registration by the user.
* If there is a persistent connection that
pushes notifications say over HTTP2, let's use that instead of
having to hop over web hooks.
* Actually we can do changeList retrieval but we'll have to
implement polling AFAIK unless there is some magic sauce
as point 2) is hopeful about.