Fixes race condition: for text stream responses, guarantees that
header is printed before the stream data.

Added MEDIA_TYPE and VENDOR columns to TAPE table and upgraded xrootd-ssi-protobuf-interface to v0.29

Usage: cta-admin --json <command> <subcommand> <options>

For stream commands only (where each line of the result is sent back in
a protocol buffer), return the results in JSON format instead of a
text table.

Adds better cleanup of Requests. The Send() method is synchronous as
before, for Metadata requests. The new SendAsync() method is for Data
and Stream requests, where the Response is returned asynchronously.

The framework now provides a DataFuture object for the asynch case.
After the Request has been sent, call DataFuture::wait() to clean up the
Request object once all data has been received.

Added partial support for repack queueing in scheduler database,
scheduler and CLI.

This reverts commit 5cda9ec6.

Done

Better to have all formatting on the client side, so we format the
header and the reponse values in the same place. (Also no need to
send this data over the wire as it's always the same).