Remove Platform Source and Reaction

The Platform Source/Reaction were a quick and dirty experiement to see how Drasi Server could be used as an alternative Query Host in Drasi Platform (D4K8S). They connect directly to Redis quees with message formats that are specific to D4K8S and are unusable for any other purpose. Goal: Move both Platform Source and Reaction out of drasi-core and unpick any depencency platform has on them. Acceptance: - Platform Source and Reaction removed from drasi-core - Drasi Server and drasi-lib tests work - Drasi Server and drasi-lib docs updated - Drasi 4K8s working without the need for the Platform Source and Reaction.