Fixes #160 with non back compatible changes.

Renames all ability events as following:

* AbilityEvent -> CommandEvent
* AbilityEvent -> BasicCommandEvent
* TargetAbilityEvent -> TargetUnitCommandEvent
* LocationAbilityEvent -> TargetPointCommandEvent

As such, all references to these classes, statements that check the event name,
and engine plugin event handlers need to be renamed. Its not ideal but it is
much better than being wrong.