Allow appointment booking to read class calendar Merged

As the software stands, a parent could book a private lesson when a class is scheduled in the studio, as it does not register that the studio is booked. I had an "extra class date" scheduled on a Sunday, and it allowed a parent to book an appointment because it can't tell that the studio is booked.

Having to remember to remove teacher availability when things are happening in the studio increases admin time significantly, and it's easy to oversee.