Display "Registration is closed for this event" message on event info page if we are outside of valid registration dates

... AND if user would otherwise have permission to register for this event.

NOTE: We do NOT want to display this message for cases where the user session does NOT have permission to register regardless of registration date constraints.
NOTE: This will require changing CRM_Event_BAO_Event::validRegistrationDate to just check for date range and adding hasPermission() call in EventInfo and Core/Block. The "registration closed" text can be defined in EventInfo.tpl so that it's easy to customize.