* Break out events and add individual handlers
https://github.com/BentoBoxWorld/BentoBox/issues/1613
* Corrected AddonEvents to have proper static handlers
* Made constructors protected.
Abstract classes should not have public constructors. Constructors of
abstract classes can only be called in constructors of their subclasses.
So there is no point in making them public. The protected modifier
should be enough.