Remove demo spec with AdHoc system

There are live tests that can be used as examples now, so this one is no
longer needed.
Calculate time traveled as departure - arrival

This doesn't often make a huge difference in the calculated values, but it
could for certain systems with long dwell times. This is closer to how
it is specified in the PDF (although it deviates from how the SQL
calculates it).
Move TimeTraveledStops tests to separate file

And added tests using the AdHoc system.
Merge pull request #270 from WorldBank-Transport/feature/time-traveled-tests

Add tests for time traveled between stops