View maps for multiday trips.

[eshika]

This CL completes the basic multiday trips feature.

List of Changes:

1. Add date input to maps page for users to enter which day of the trip they want to see.
2. Add date query parameter to the fetch request in the front end.
3. Query datastore to get the tripDay associated with the tripKey parameter and date parameter in the backend.
4. Send a fetch request with the inputted date as a parameter when the date input is changed.
5. Make the maps page show the route for the first day of the trip as a default.
6. Update tests for multiday changes.