Add activateFully() to class Persistent:
- Will be needed for serialize() in Score/Trust - serialize() will need to activate the truster/trustee Identity object fully
- Use it in OwnIdentity/Identity/Score/Trust
Move serialization code to class Persistent:
- The serialize()/deserialize() functions would have wound up to be almost completely identical for Score/Trust so we should have them in Persistent
- Execute startupDatabaseIntegrityTest upon deserialization in an assert to check whether serialization works properly