EZP-23437: added specs/doc for DFS
EZP-23437: Added DFS metadata handler
EZP-23437: Added listener to serve binary files
EZP-23437: DFS ConfigurationFactory
EZP-23437: Registered legacy_dfs_cluster to the extension
EZP-23437: cleanup + license headers
EZP-23437: Changed SPI mtime to DateTime

Was supposed to be this way :)
EZP-23437: Pass url_prefix to stream listener directly
Merge pull request #1031 from ezsystems/EZP-23437-dfs_io_handler

IO: Added DFS metadata handler