Extend Network Package format to include Aux. Transit Volumes

[King-David]

The walk volumes on links are a key QC parameter used by Metrolinx within PD 1, especially around Union station. Currently the auxiliary transit volumes are not exported with the NWP and I ask if this feature could please be added.

Thank you.

[PeterKucirek]

Thanks for taking care of this enhancement. I was going to make an attempt but I don't have the time this week. Just a couple of notes based on your latest commit:

• _batchout_traffic_results(), where you've added the code to export the aux. transit volumes, only gets called when there are traffic results. So this could potentially fail if, say, the scenario has a transit assignment but not a traffic assignment
• You'll need to update import_network_package.py as well.

[BrendanReilly]

@PeterKucirek The most recent commit addresses the issues pointed out in your comment.