Add reading of archive files from DFS

Currently, the manifest of archive files can be read from DFS, but the archive files themselves are read via the Java URL class (deep down in ArchiveReader) which does not know how to read from DFS by default.

We should add a URLConnectionHandler for DFS so that we can read archive files from it. Something like

dfs://server:9000/path/to/file.arc.gz

would probably work.