File writing

The filewriter is responsible for taking the neutron and SE data out of Kafka and writing it to a nexus file. When the ICP ends a run it sends a config message to the filewriter, via Kafka, to tell it to start writing to file.

There is also a filewriter written for the SuperMuSR project which we may choose to use. This will be decided in this ticket

We are currently figuring out topology on how to run this, ie one-per-instrument or centrally. This is being done as part of the MNeuData project generally, but for HRPD-X we will decide this in this ticket