Create sniff for event declaration validation

[aik099]

For every event method (method name starts with On and 1st parameter is called $event, class name has EventHandler) we need to:

1. validate, that method scope is protected (empty scope considered public)
2. validate, that $event parameter type hint is kEvent
3. analyze method DocBlock (if present) to:
   • have @return void
   • the $event parameter declaration to be @param kEvent $event Event.