- VObject fixes for Sabre\VObject 3.3
- Remove VObject property workarounds
- Added prefetching for tags in sabre tags plugin
- Moved oc_properties logic to separate PropertyStorage backend (WIP)
- Fixed Sabre connector namespaces
- Improved files plugin to handle props on-demand
- Moved allowed props from server class to files plugin
- Fixed tags caching for files that are known to have no tags
  (less queries)
- Added/fixed unit tests for Sabre FilesPlugin, TagsPlugin
- Replace OC\Connector\Sabre\Request with direct call to
  httpRequest->setUrl()
- Fix exception detection in DAV client when using Sabre\DAV\Client
- Added setETag() on Node instead of using the static FileSystem
- Also preload tags/props when depth is infinity

The encryption webdav tests are too broad and do not qualify as unit
test. Also, since the sabre upgrade they are not fixable.
The matching functionality is already tested in other classes on a
smaller scale.

Reasoning:
- a WebDAV server is not required to implement locking support
- WebDAV Locking is know to break the sync algorithm
- the current lock implementation is known to be broken (locks are not moved if a file is moved, locks on shared files don't work)