DESCRIPTION:

REGISTER an event handler.
Event handlers can be applied on different scopes:
- [G]lobal, if the event should fire for all views and renderers
- [E]ngine, if it should only fire for views using a specific
  renderer engine
- [V]iew, if it should fire only for a specific view.
- [R]enderer, if it should only fire for a specific renderer
Type tells which kind of event to react to:
- [m]ouse events. See REGISTER_MOUSE.
- [k]ey events. See REGISTER_KEY.
- [c]ommand events. See REGISTER_COMMAND.