implemented get hashcode and cleanup

lib/models/ingredient.dart

@@ -16,4 +16,9 @@ class Ingredient {
     Ingredient i = other as Ingredient;
     return title == i.title;
   }
+
+  @override
+  int get hashCode {
+    return Object.hash(title, null);
+  }
 }

lib/models/ingredient_list_entry.dart

@@ -14,4 +14,9 @@ class IngredientListEntry {
     final i = other as IngredientListEntry;
     return ingredient == i.ingredient;
   }
+
+  @override
+  int get hashCode {
+    return Object.hash(ingredient, null);
+  }
 }