admin availability null error, can't navigate from staff -> sched (staff loads different panels) pop ups still need to be hooked up

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

Fixed a bug where isManager wasn't properly evaluated, and changed how positions in the employee are separated.

Added comments, and added a method to receive the availability of a new employee. Also fixed a bug in the splitting of some data.

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.