Include implementation of dropboxstorage from Cedric Leninivin
Fix manual query trigger condition.
Missing methods
Handle concurrent deletion while fetching all documents
Change davstorage model to support all documents.

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.
Drop "command" parameter from the previous jio version.
Move blob reader promises
Return more verbose error messages
Allow to dynamically change webdav data model.

Each webdav file is transformed as a single "enclosure" attachment to a jio document with the same name.
Optimitic write back cache storage.

This cache doesn't have any conflict detection and can lead to data lose.
Include more storages in jio build.