Feature-ish: Introduce (unused) generic EventManager class
Codechange: Reorder EventManager interfaces

Extract another interface layer from EventManager classes.
Rename IEventManager subscription interfaces to IEventSubscriber
Have new IEventManager implement IEventSubscriber and IEventInvoker
Feature: Introduce new TypedAndGenericEventManager plus interface
Feature: Add option to register a type for an event handler
Feature: Allow id-based event subscriptions
Codechange: Utilize the new id-based event system
Feature: Add overloads to RequestData that subscribe a callback for a given ID on the way