Added a clause to the add shift method that checks the availability and makes sure that the start is later than the end.

Added the ability for you to check into a shift by passing the shift ID. If you sign in you should know who the employee is and what shifts they work that day. The methods sign you in if you sign in over five minutes early or over five minutes late, in which case you must talk to a manager and they should change your shift to the hours worked.
Also, added a function for calculating the number of hours worked.

Added functionality for availability and requesting time off to the app. The app needs at least one employee in the database to run. Make sure to open the sql file in the repo drop your current table and execute everything from "create database" to the end of the availability table.

Employees table now captures the email, phone number, isManager, and wage.
Shift table now captures the availability of the shift. Updated parsing so all employee and shift details are separated by commas.

Changed the employees and shift collections from both being ArrayList<String> to HashMap<Int ID, Employee> and HashMap<Int ID, Shift> respectively. Refactored all methods that used the old employee and shift collections. Cleaned up some warnings.

Changed print all employees to remove the 'allEmployees' part. And made a function for getting the number of staff.