Proper injection of filesystem view into the webdav connector

First part of the work on #7221

This makes it easier to use the webdav connector to expose other parts of the filesystem over webdav such as public shares.

Besides the view injection this also changes the webdav connector to use the FileInfo object for caching the file metadata.

Tested with litmus and some basic webdav usage with dolphin, needs additional testing for the owncloud specific webdav bits such as chunking, etags, etc (@dragotin)

cc @karlitschek  @DeepDiver1975 @PVince81