Fix up event names and hierarchy.

* PacketEvent is now ProgressEvent.
* SetToHotkeyEvent is now SetControlGroupEvent.
* AddToHotkeyEvent is now AddToControlGroupEvent.
* GetFromHotkeyEvent is now GetControlGroupEvent.
* PlayerAbilityEvent is no longer part of the event hierarchy.
* event.name is no longer a class property; it can only be accessed from an event instance.
Flesh out the ping class.
Misc. documentation improvements.