Managing Node's memoryleaks with a node:destroy event

[ItsAsbreuk]

Actually, this is a whole picture of managing memoryleaks related to Node.

It also consists issues
#547
#549
#560
#551

which can be closed if you fulfill this ticket in some way.

The proposal consist of 4 steps to be made:

1. introduce the node:destroy event
   Node.destroy() should fire a node:destroy event.
   Node.removeChild(childnode) should fire a node:destroy event for childnode.
   Node.replaceChild(node, refnode) should fire a node:destroy event for refnode.

Also, Node.load, Node.setHTML, Node.remove and Node.replace are safe now, because -under the hood- they use some of the three method mentioned before.

2. Make the eventsystem in a way that all events are listening to the node:destroy event by themself. Once they catch such an event: they need to look up in the domstructure whether the node that fired the node:destroy-event is a parentNode of the Node it was bound to itself. If so: the eventlistener should destroy itself (detach). This way, none of the Node-methods need to have recursive option anymore!

3. Make Widgets standard listen to node:destroy by design. Once they catch such an event: they need to look up in the domstructure whether the node that fired the node:destroy-event is a parentNode or if its the widgets-boundingBox. If so: the widget should destroy itself.

4. Define a YUI_config option 'memorySafe' which takes care of Node._instances to do a cleanup when Y.on('node:destroy') is fired. The cleanup should exists of cleaning the Node._instances with all references of the destoyed Node, as well as its children. Because this has a performancehit, 'memorySafe' should be made an option. Anyone who need speed can set this off while anyone who need a rocksolid app can set it on.