User management

[WanWizard]

Any access beyond read-only will require a login. Suggested is to use github accounts only for now.

The system needs to support groups, and ACL,s on groups. It needs an admin backend to be able to do the user administration. ACL's on authentication method might be a nice feature for future use.

[dberry37388]

I would probably throw in twitter accounts for log in also...

[tomschlick]

I already have the github login working for cells. We can port that logic as soon as I remove the redirect loop bug.

[WanWizard]

I think we should require a github account for cells, hence my remark for ACL's linked to the authentication method. For other purposes, we can add other authentication methods later.