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
I had that in mind but I chose not to. The token name can be any string value, it is just a *name* used in only a few places, That value it is defined in the config for a *separate bundle*. It is not likely that we should try to guess that the value of this parameter should be 'google_drive'. I'm more likely to name my tokens: 'tobias_account', 'company_accout' etc. 

I believe it is more important to write good documentation to educate the developers so they understand what the token name is and where it is defined. 

If we have a default value and the user forgets to set the correct token name he/she will get an exception when running the code instead of a configuration error.