Add time_of_week field to schedule model.

Add schedule factory.
Add join table for ScheduleRoutes.
A schedule has one route.
A route has many schedules.

Add byebug gem.
Add join table for ScheduleStops.
Add timestamps to join tables.
Add more validation to schedule model.
Add specs for direction validation.
Add shared example for numeric fields.
Add spec for timetable row and time of week.
Add validation to association fields.