Integrate GTFS shifting functionality

[sebhoerl]

For many use cases, we need to match GTFS schedules. We already have automated this functionality. However, sometimes, we have cases in which the schedules don't overlap, so one or multiple will be ignored because no common date (the one with most services by default) can be found. @tkchouaki has developed the code to shift the schedules such that all of them cover the same date for a specific weekday. This code should be integrated here in the pipeline.