Add filter to show services for a specific station

[peter-mount]

Originally part of #23 we need a dest= filter which takes a CRS code and return just those services which will either call at or were due to call at that station.

Unlike callsAt= which has been done as part of #23 this one has to be able to show services that have been cancelled. callsAt works on the calling points list but that doesn't show stops that have been cancelled and for some users like UK Rail Departure Boards they would want to know if a service to their required station has been cancelled - callsAt would just not know about it.