Removed copy in flag.pad() when running dict.populate()
This PR fixes a bug in DataQualityFlag.copy()
that would miss attributes that weren't explicitly named, and adds an inplace
kwarg to DataQualityFlag.pad
to modify the active and
known` segmentlists in place, instead of returning a copy of the flag.
This is done to allow DataQualityDict.populate
to not copy flags when padding is used, meaning the values are the same objects before and after this method is used.