run and event header parsing

Currently event sources only handle PMT, MTC, and CAEN data.

Run-level and event-level headers must be handled, too, and make their way to interested apps such as the event viewer.

This data may come from the ZDAB dispatch stream, the OrcaJSON stream, a CouchDB changes feed, or all of the above. Care must be taken to ensure that we accept and store a given piece of data from one source only.
