First draft fo the event system, alex wants to do further work
Event-system: added getEventType to EventHandler
Added EventDispatcher#remove method
Renamed HasHandlers into HasEventHandlers and put into gui.event root
* New EventListener, because an EventHandler had previously two tasks,
  declare a `onEvent` method and deligate a event of this type to the
  `onEvent` method, now the EventHandler deligates an event to the
  EventListener and the EventListener declares the `onEvent` method
* added EventHandler#dispatch and fixed EventDispatcher#dispatch
Added a TestCase for the event flow in the event system
Reworked the event structures as i described during the session. The need to change the eventDispatcher when adding eventtypes has been removed, there is one generic addHandler method. also the listener/handler doubling has been removed -- i still dont know what they were for. handler and listener are synonyms i think. Since an event GETS dispatched, it is now a method of the specific event class. there is no need that event handlers (those who want to receive events) need to know how to dispatch events, this is centralized in the eventdispatcher. since firing an event and dispatching it are two different things, the HasEventHandlers interface was corrected, dispatching in EventDispather is now done is a type safe way, types get checked during add-method. the HasXHandler interfaces are now optional for abstraction of classes that allow to add handlers dynamically.
corrected modified of internal fireEvent method of dispatcher. adjusted testcase for implementation
senseless final modifiers introduced as implicit documentation (yeah)
removed unused interfaces, code is getting thinner
reworked dispatcher and event dispatching in Event class s.t. classes are not passed explicitly as event types
added documentation of the general event mechanism
added documentation of the first gui event created: the Symmetry3DChoose event, which is invoked when the user chose a new 3d symmetry in the symmetry chooser panel