Move down to only 1 abstract data type with a nully Frequency. Should aid in making the Expense page usable for all 3 data type.

lib/db.dart

@@ -9,7 +9,7 @@ import 'package:sqflite/sqflite.dart';
 
 // Local
 import '/models/expense.dart';
-import '/models/tracked_type_recurring.dart';
+import '/models/tracked_item.dart';
 
 // Leaned on this example:
 //   https://learnflutterwithme.com/sqlite
@@ -77,7 +77,7 @@ class DatabaseHelper {
     return expenseList;
   }
 
-  Future<int> addExpense(RecurringTrackedType expense) async {
+  Future<int> addExpense(TrackedItem expense) async {
     Database db = await instance.db;
     return await db.insert(
       "expense",
@@ -94,7 +94,7 @@ class DatabaseHelper {
     );
   }
 
-  Future<int> updateExpense(RecurringTrackedType expense) async {
+  Future<int> updateExpense(TrackedItem expense) async {
     Database db = await instance.db;
     return await db.update(
       "expense",