Model/View system mostly working for Entity editor
Editors now subclass QtGui.QWidget

As children of the QtGui.QWidget class, editors can now more easily
be shown or hidden, which will be useful if the editing panes are
broken up into multiple windows in the future.  Additionally, each
editor may now subscribe to and emit signals using PyQt's slot/signal
system.
Back to item-based widgets rather than model/view.  Added Event system.