Draft: Add hit writer

I'm trying to implement a hit writer that looks like our everything-else writers, as demanded by #178. There's a bit to do:

• Add an instance of the hit writer to the JetLinkWriter options
• Add output options in the dumpster json
• Add customConsumers for the hit variables
• Add a hit associator python block
• Make a working json config

The first part was super easy because I realized that we don't do any selection for associated objects in most cases, so dumping whatever we associate might just work "out of the box" for non-custom variables.