Address participant_in_activity_or_association

[GCHQDeveloper42]

There is one extra Java class in the HQDM package due to the conversion process from EXPRESS generating a Java class for the EXPRESS decision block "participant_in_activity_or_association". It is included as a Java Class but its use is open to interpretation (and it doesn't map neatly to RDFS/OWL). Activity and association patterns are commonly needed so cleaning this up would help consistent use of these patterns.