When a session is modified with Edit Current Session, it retains a link to the original profile and changes in the original profile will be reflected in the session except for values changed in Edit Current Session. Also fixes a bug where semantic history's editor would not be initialized correctly for such sessions. Fixes a bug where sessions restored from arrangements would lose the link to the underlying profile.
Clean up PreferencePanel.h somewhat and make changes to a divorced session's profile caused by a change to the original profile be reflected in the Edit Current Session preference panel