Add option to (locally) use different bell schedule when using shared school

[amah853]

Whoever owns the shared school picks the bell schedule for each day, but give the user the option to instead use a different bell schedule for themselves for whatever reason (selected bell schedule for that day is wrong, etc.)

[nicolaschan]

This is an awesome suggestion! I hadn't thought of this but this is a great way to handle when the schedule maintainer forgets to input exceptions to the weekly schedule. I'll keep this in mind for a future update.