Updated behaviour of known segments for DataQualityFlag logic operations

This PR modifies the behavour of the known segmentlist during DataQualityFlag logic operations. The thinking is that the result of a logic operation should only be 'known' when both of the flags (on either side of the operator) were known, with the exception of 'or' (|, union), where either flag can be known.

One example of where this is important is when subtracting hardware injection segments from observing segments. If there is a gap in the knowledge of the injection flag then the result of observing - injection should only be known (or active) when both the observing and injection flags were known, just in case an injection was present during the gap in the knowledge of the flag, or similar.