Add function to get the current active step index

[iswheeler]

In the steps UI (accessible via swiping up), we need a way to see where the user is within a stage (i.e. "You've passed the first two bus stops and there are three more to go"). Please come up with a function inside BusStage that returns the index (e.g. 2) of the last step passed. (integers--don't worry about fractions for now)

[iswheeler]

Please also add a getFixedTitle() function that returns a title summarizing your stage (e.g. "Ride 4 stops")--this is so it can be displayed in the swipe-up steps view.