WebDAV support / Mutable body

[dantleech]

I wonder to what extent we could support WebDAV, for example via

https://github.com/fruux/sabre-dav

Ultimately this would allow people to mount the repository tree locally as a filesystem.

If we support [get|set]Body then we could support remote authoring / template design.

For example if Twig templates could be stored in the ORM, PHPCR-ODM or even on the filesystem (!). A document/entity would only need to implement a MutableBody interface and a designer could modify remote templates in a local editor.