add onOwnerChanged as default method + comment
smarter EventHandler>>registerHTMLAndSVG, unregisters automatically
this fixes a memory leak: only register event handlers when morph appears in
world, unregister when morph isn't visible anymore
event handler mem leak fix: also get rid of then handler func
event handler mem leak fix: fixing world eventhandler init
better automatic unregistering of event handlers
Merge pull request #123 from LivelyKernel/fix-event-handler-mem-leak

Fix event handler mem leak