Nbextension

Make it a nbextension.

That would allow to use gdrive from many profiles, and is cleaner for upgrades

This **try to** use the [relative module name trick](http://requirejs.org/docs/api.html#modulenotes) so that we don't have to hardcode the location of gapi_utils and drive_utils location.

It does work in some places, but not other, I don't get why.