Implemented methods in AddExpense and Expenses such that information flow occurs between the two classes

Created new Expense Controller, renamed old Expense Controller to ExpensesController, and created two other new controller classes for testing

Commented out sections of code relating to expense overview. Connected all fxml files to the same controller

Implement initializable in controller. Added methods that switch to expenses window and adds expenses

Here is a version where the program finds the fxml file and runs correctly. Nothing after first window popup