Add a button function to POS to send out a negative balance alert via email.

This function would speed up the process in alerting parents their child's account has a negative balance on the day the balance becomes negative, instead of waiting at the end of the week to send out notices.

To give the cashier the ability to send a parent a negative balance alert at the time their child is at the register & their account goes into the negative. It would send an alert to the parent's email on file.