Add generics to EventBus

[skiwi2]

EventBus should use generics, such that it becomes an EventBus<T>.
The requirement to provide the class literal should be voided.

Example implementation:

• Add a method getEventBus() to EventBusFactory, which infers the type T, this should create an instance of EventBus<T>, if possible without explicitely supplying T.class.
• As a result both SimpleEventBus and VoidEventBus become private static inner classes of EventBusFactory.

It is imperative that the unit tests should be updated accordingly aswell.