view / modify availabilty should work, needs more testing

.../main/java/com/example/schedulerapp/AvailabilityView.java

...pp/src/main/java/com/example/schedulerapp/Controller.java

...rApp/src/main/java/com/example/schedulerapp/Employee.java

...ulerApp/src/main/java/com/example/schedulerapp/Model.java

...ces/com/example/schedulerapp/availabilityBottomPanel.fxml

...resources/com/example/schedulerapp/availabilityPopup.fxml

...urces/com/example/schedulerapp/staffManagerSidePanel.fxml