This storage will transparently compress getAttachment/putAttachment results.
Only text, json, xml mme type are compressed.

Thanks to Lucas Parsy.

Synchronisation status is based on document signature (sha) comparison.
Signature are stored each time a document is successfully synchronised.

Conflict are detected but reported as an error for now, as no solve process is implemented.

Simplify storage and tests code.

Change the database structure so that the "attachment" store contains one entry per attachment.

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.

See docs/query.rst for more informations

To avoid phantomjs (or headless webkit) bug.