Fix #131

Added these to MMAL translation. No idea what privacy indicator does
(and the parameter struct's definition seems incomplete). Render stats
seems to work happily with the preview component's input port, but I've
no idea what any of the struct's fields actually mean at the moment. For
now, I'll mark this as complete until such time as I can dig up some
info on the meaning of the fields at which point it should be easy to
add some meaningful properties to PiCamera for querying this.