CHANGE: Success rates for buildings now depend on the proportion of passengers transported to their first and second choice destinations: success is reduced to 75% for passengers' second choice destination, and to only 50% of what it would otherwise be for their third and subsequent choices.
Merge branch 'walking-passengers' into private-cars
CHANGE: Do not show a red dot (overcrowded) in the passenger destinations display unless the overcrowded stop could have got the passengers to their destination if it was not overcrowded
CHANGE: Do not show return trips in the passenger destinations map display (for clarity)
FIX: Division by zero crash in the private car route finding algorithm.