An abstract Storage abstraction class is added.
There will be a factory to instantiate concrete
implementation for a given backend.
For WebDAV and similar hosted backends, authentication
and authorization will be done by the implementation
with the help of the Auth abstraction.
Change-Id: I38ec5dad4c2c4ce16df30d65826df96751b10e2d
Reviewed-on: https://gerrit.libreoffice.org/22513
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>
Tested-by: Ashod Nakashian <ashnakash@gmail.com>
