Overbooking issue

[Janez Svetin]

Another issue which fix for issue #72 does not solve is overbooking. Additional checks need to be programmed which validate if, for example, staff is on two appointments at the same time and rules do not allow that. Or, for example, if the general rule allows only two appointments in time range but there are three etc. Let me know how to fix this. In my opinion, implementation should be similar to the validation (fix for issue #72).

[Željan Topić]

Fixed.