Bell Schedule Creation Endpoint will crash if not provided with a school ID in the request body

[MoralCode]

ClassClockAPI/blueprints/v0.py

Line 423 in 06108fe

school = SchoolDB.query.filter_by(id=school_id).first()

this can be reproduced by creating a schedule without selecting a school in the admin UI.

This should return at LEAST a sane error message on the backend.
The frontend should also include validation to ensure the form cant be submitted without specifying a school.