IO: add Archive support to Filesystem class

[mgerhardy]

We should directly create ReadStreams in the Filesystem class and also be able to register Archives here - this would allow for other directories (FilesystemArchive) but also for zip files (ZipArchive) to be registered and read from without unpacking the content. This is e.g. used in voxconvert for --input - here we extract the whole zip file to operate on the files.