fix handling of harmless InterruptedException during shutdown

this could happen if we blocked on a read from the journal, and the server shut down.
other exceptions will be rethrown

the exception handling code is slightly awkward because the kafka scala code doesn't declare the IOException so the java compiler thinks it won't ever be thrown (fun eh)
add journal decode command, improve journal show

journal show now displays:
 - number of messages in the journal
 - the first offset in the journal (useful for use with journal decode)
 - the actual last offset (not the next offset after the end of the log)

simple version of journal decode
 - allows printing metadata about the message
 - uses the actual codec to parse the RawMessage from the log

overriding the codec or dumping the raw values including all metadata is not yet supported (neither from RawMessage nor from Message)