Adding Google Drive

This is work in progress. I'm not too sure with the authentication part... will work on that... 

### Other notes
I added a interface for clients. We may want to create a `ClientProvider` of some kind. One may also want to simplify the configuration. (But this is out of scope for this PR)

### Resources: 
https://developers.google.com/accounts/docs/OAuth2
https://developers.google.com/drive/web/quickstart/quickstart-php
https://developers.google.com/drive/web/auth/web-server
Agree. 
This is a suitable choice.