Fixed unicode and python3 support in Hubic driver and tests.
Updated list of functional features for Hubic tests.
Refacto of the Dropbox driver

- Complete refacto of the change polling thread to make it more
maintainable

- Removed useless functions (stringify) and unneeded Unicode 'u's
More Dropbox refacto

- Deal with longpoll_delta backoff
- Some u's were still missing
- More debug logging
Use the new syntax for the setup. Entry -> Service

- Parse the new setup with folders and services
- Put the folders in the db
- Rename every occurence to entry to service
- Update the API routes to use services
- Rename Plug.entry_db to Plug.service_db
- Update the tests to use services
- Remove the rules in the Referee
- Remove the rules in the tests
- Root is no longer an option but a property
- Update the drivers
Use PUB/SUB for Referee's notifications
Temporarly remove .travis.yml to avoid builds
Add Folder class to the Plug
Add Plug.folders
Add folder to Metadata and remove owners

The fid is now calculated from the current folder and the
filename.
Update Plug.get_metadata to handle folders
Metadata.path return the full path of the file
Fix folders initialization in the Refree
Referee: Fail gracefully if there is an error
Referee: Adapt handle_update to the folders
Handle deletions with folders
Fix Metadata.fid
Delete the metadata after the call to delete_file
Handle moves with folders
Add a Folder class to the Referee