CR Schedule View: Display basic timetable

[lemald]

Summary of changes

Asana Ticket: part of 🏹🚆 Schedule View

This change handles the basics of rendering the schedule into a tabular timetable view, while also allowing toggling between different routes and directions within the same export. The page is still not linked directly from the Trainsformer export section, but you can manually navigate to /trainsformer_exports/[export ID]/timetable in your browser to look at the rendered result.

Note that I am aware that the ordering of the stops when not all trips have the same stopping pattern isn't great. I think improving that will be for a followup PR / subtask.

Reviewer Checklist

• Meets ticket's acceptance criteria
• Any new or changed functions have typespecs
• Tests were added for any new functionality (don't just rely on Codecov)
• This branch was deployed to the staging environment and is currently running with no unexpected increase in warnings, and no errors or crashes.