dillon1000/react

Create `EventPluginRegistry`

The `EventPluginHub` module was getting huge and scary. This pulls out all of the logic required to inject plugins and publish their event registration names into a new `EventPluginRegistry` module.

Functionally, nothing should have changed. I added many error checks to cover edge cases that we were not yet running into, but they are all in `EventPluginRegistry` and unit tested.