Merging stop_order into develop branch

[lmz]

Major changes are:

1. Add the latest-departure-trip to the stop state and don't allow the same trip in labeling the next stop. Since the latest-departure (and its trip) define the time window, during the labeling, we don't want to assume we can use the same trip again for the next link label, because if we choose it, we'll be forced to choose it again.
2. When we update the stop state for a stop that's already been processed, it may affect other reachable stops, so mark it to reprocess (by putting it back on the label queue).
3. Make the label queue smarter: if we add a stop1, labelX then stop1, labelY, only the lower label is valid. So a stop can only be in the queue once at any given point in time.
4. Make the maximum number of times a stop can be processed a configurable number. (So setting it to one is similar to the previous version of this code.)
5. Return and write basic performance measures: milliseconds spent doing labeling, milliseconds spent doing enumeration, number of labeling iterations executed, maximum number of times a stop was processed.