ACL - Work in progress

The branch is almost ready.

* [x] We already unit tested the backend to be able to implement other backends.
* [x]  We still need to make sure that the views tests passes.
* [x] We would like to implement the persona backend.
* [x] Add a token-based authentication
* [x] Make the tests use a different authentication than persona.
* [x] Rebase / Merge with master.