SSP Validation: Skip bad trips

[irees]

When a trip contains bad schedule data, e.g. goes backwards in time, skip the trip entirely & log error. Continue on to other trips.

See: http://transit.land/dispatcher/feeds/f-udt-Петербургский~метрополитен

[drewda]

@irees was this resolved by #1163 ?

[irees]

@drewda #1163 takes care of one type of bad trip - missing some required time points. I could add more types of bad trips, such as the referenced feed above where times go backwards, but we can go ahead and close this issue.

[drewda]

@irees o.k., makes sense to keep this open until there's reason to gracefully handle backwards times