Add ability to stop the propogation of events

How do you feel about allowing people to do something (like `return false`) in an event handler to stop pixi from continuing to call events other hit elements (like stopPropogation).

Basically in an isometric map if I hover over a tile, it will go "through" that tile and hover a bunch of them; but it would be nice to `return false` on the first one so only the events are called for one.

In this PR I implemented the `return false` means stop checking methodology, but I wanted to see what you thought and if there was a different way you wanted to handle this.