Dav directory is represented as one jio document.
Its files are represented as its attachment.

This allows to start from a non empty webdav (with music, pictures for examples)

Alldocs is not implemented for now but subdirectory can still be created.

Enough for now to force usage of querystorage and simplify allDocs everywhere else.

This is a work in progress commit and all storages are broken.

* Use as much as possible RSVP promise to simplify the code.
* simplify error management: use Error class in case of problem.
* Drop the job management at that point. Such functionnality could be reimplemented as a storage.
* Start to simplify the tests, to speed up debugging.
* Drop requireJS usage, as the goal for now is to make it usage on browser.
* allDocs has to be rewritten to ease storage tree capacity checking. A storage should only implement what it could really do.
* disable attachment management for now.