Adding PropertyChangeListener interface to UserProfileManager (and a
required helper class) to handle persistence of changes to the
UserProfile, improving interface documentation, replacing assertions in
SctTreeCell with isolated object access to throw more readable
NullPointerExceptions, adding warning to SctTreeView init() in case root
concept chronicle returned by getFxConcept() has no destination
relationships (likely caused by bad relationship assertion value in
ViewCoordinate)