Clean up to get out of WIP
Clean up to get out of WIP

* Remove legacy ShouldComponentUpdate logic
* Flow types for props and metadata props
* Rather than pass an empty non-functioning function as the default onMetadataChange function, just check for the existence of such a function and only run it if it exists

nteract/nteract,nteract/nteract,rgbkrk/nteract,nteract/composition,nteract/nteract,rgbkrk/nteract,nteract/nteract,rgbkrk/nteract,rgbkrk/nteract,nteract/nteract,nteract/composition,nteract/composition,rgbkrk/nteract