refactored props to be a per-object configuration object
Removed all the ALLCAPS class constants, and replaced them with calls
to a props object. This meant modifying the class constructors and class methods
to take optional Props objects, defaulting to Props.defaultProps object. The
Props.defaultProps object isn't officially a singlton but since there are no
intermediary ALLCAPS constanst and all Props objects are event emitters when
you use props.setMetaProps() everything should be mostly ok.