[WIP] New rules

This PR is a Work-in-Progress for the implementation of the new rules systems (which ironically doesn't have the notion of 'rules' anymore).

You can find more information [here](http://onitu.readthedocs.org/en/latest/configuration.html) or in the issue #85.

Progress : 
- [x] Parse the new setup
- [x] Entry -> Service
- [x] Use PUB/SUB in the Referee
- [x] Accept YAML for the setup
- [x] Update the Plug and the Referee to work with folders
- ~~[ ] Support embedded folders~~
- [x] Adapt the tests
- [x] Write basic tests
- [x] Support conditions in the Referee
- ~~[ ] Support modes in the Referee~~
- [x] Adapt the API
- [x] Adapt the drivers
    - [x] Local storage
    - [x] S3
    - [x] Dropbox
    - [x] Hubic
- [x] Handle moves between folders
- [x] Make sure the rules are re-interpreted when the metadata change
- [x] Add unit tests for the folders