Use participant consents exclusively to determine when an imported participant switches to hi intensity (#3997)

Changes the importer event/state processing to move a participant to high at the point in her event history where her consent history indicates she consented to high. Pseudocode:

     foreach event
        move_to_high_if_not_in_high_and_consented_as_of(event.some_concrete_date)
        import event
     end