* add one more callback hook to the webcit DAV handler structure; this will be used...

* add one more callback hook to the webcit DAV handler structure; this will be used to revalidate URLs, move or delete certain items referenced by URLs
* add handler vor EUID based namespaces; so far we just have the exists logic; this will be filled with the other required operations soon.
* finish REST URL parsing with 'best-guess'-room logic