Add a Rejected port to FeatureWriter

This idea has come up in the 2016 thread (now released) about adding any output ports to FeatureWriter but the use case for Rejected features remains - e.g. some web-based format has a transient HTTP error, the failed features need to be retried after a wee delay, or a field overflows and can’t be written. @markatsafe @rylanatsafe you guys were on that thread. FeatureReader has a Rejected port, very handy for retry logic in a looping custom transformer, lets see it for FeatureWriter!