MNT: Single function call to create an event

- The previous implementation formatted the event and then
  published it to an epics PV.  A server was monitoring that PV
  and then wrote it into metadatastore.  That's a stupid
  implementation (sorry!) because then data can be lost if
  the PV is overwritten before the server can grab it and
  publish it to metadatastore

- This implementation just writes the event into metadatastore
  and then publishes it to a PV.  The only possible information
  loss is in the live viewer which is not a big deal (Stuart
  confirms that this is not a big deal)