Fixed some bugs that would cause edited shifts to return nothing, and the edited availability to return nothing.

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

After a change in the database that made email addresses unique, caused a bug where new employees on the app to not be added after the first one.

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

Added a claus that checks if a position is removed from all employees during the "removePosition" case.

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

Fixed an issue with added positions if they didnt exist in the position table, and a bug after removing the last position for an employee then adding a new one.

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.