Clean up eventx core

Removed a lot of feature logic, deferring instead to default event overrides.

Base event and default event,
Y.EventTarget.configure(ClassOrInstance, eventMap, base, default);

So far, so good.
Add dynamic event feature as base and default events

Created Y.CustomEvent.DYNAMIC_BASE and DYNAMIC_DEFAULT to support publishing
events that can handle multiple types or a specific signature. Useful in
Y.EventTarget.configure(Class, events, HERE, AND_HERE).
Make Y an EventTarget

Configured with dynamic event support to facilitate DOM event subs with
Y.on(...) and other bad ideas.
Testing testing, manual testing

Can't use Y.Test because it uses the current EventTarget. Still, there has to
be a better way.
WIP. Rewriting all the things

The beginnings of Y.Event are in place, the default event code to subscribe to
DOM events. Lots yet to be done.