[wpiutil] Unified message bus

[PeterJohnson]

The ntcore LocalStorage implementation is essentially the core of a generic message bus (type-safe pub/sub with change notifications). The cscore implementation contains a similar concept (with image sources and sinks) but is not named or discoverable. Simulation is yet a third (with its own websockets interface). The concept would be to unify some, most, or all of these into a unified message bus.