Update mybutton widget to take in buttonColor & TextColour. Add Success message pop up message.

Update all buttons to include button color and text colors.

Frontend/patient_manager/lib/pages/patientAdd.dart

@@ -284,6 +284,8 @@ class _AddPatientState extends State<AddPatient> {
                         }
                       },
                       buttonText: "Add",
+                      buttonColor: Colors.blueAccent,
+                      textColor: Colors.white,
                     ),
                   ),
                 ],