List refactor (#179)

* Catch paginator bug if widget is disposed before request returns

* Refactoring paginated query widget

- Add option to enable / disable search filters

* Major refactor of paginated search widget

- Learned something new.. a state can access widget.<attribute>
- THIS CHANGES EVERTHING

* Preferences: Add code for tri-state values

- Also improve unit testing for preferences code

* Allow boolean form fields to be optionally tristate

* paginator: Allow custom boolean filters

* Remove outdated filtering preferences

* Refactor filter options

- Allow specification of more detailed options

* Add custom filters for "part" list

* filter tweaks

* Remove legacy "SublocationList" widget

* Add filtering option for locationlist

* Updates for stock location widget

* Refactor category display widget

* More widget refactoring

* Update main search widget

* Fix unit tests

* Improve filtering on BOM display page

test/preferences_test.dart

@@ -8,7 +8,6 @@ import "package:inventree/preferences.dart";
 void main() {
 
   setUp(() async {
-
   });
 
   group("Settings Tests:", () {
@@ -26,5 +25,44 @@ void main() {
 
       expect(await InvenTreeSettingsManager().getValue("abc", "123"), equals("xyz"));
     });
+
+    test("Booleans", () async {
+      // Tests for boolean values
+
+      await InvenTreeSettingsManager().removeValue("chicken");
+
+      // Use default values when a setting does not exist
+      assert(await InvenTreeSettingsManager().getBool("chicken", true) == true);
+      assert(await InvenTreeSettingsManager().getBool("chicken", false) == false);
+
+      // Explicitly set to true
+      await InvenTreeSettingsManager().setValue("chicken", true);
+      assert(await InvenTreeSettingsManager().getBool("chicken", false) == true);
+
+      // Explicitly set to false
+      await InvenTreeSettingsManager().setValue("chicken", false);
+      assert(await InvenTreeSettingsManager().getBool("chicken", true) == false);
+
+    });
+
+    test("Tri State", () async {
+      // Tests for tristate values
+
+      await InvenTreeSettingsManager().removeValue("dog");
+
+      // Use default values when a setting does not exist
+      for (bool? value in [true, false, null]) {
+        assert(await InvenTreeSettingsManager().getTriState("dog", value) == value);
+      }
+
+      // Explicitly set to a value
+      for (bool? value in [true, false, null]) {
+        await InvenTreeSettingsManager().setValue("dog", value);
+
+        assert(await InvenTreeSettingsManager().getTriState("dog", true) == value);
+        assert(await InvenTreeSettingsManager().getTriState("dog", false) == value);
+        assert(await InvenTreeSettingsManager().getTriState("dog", null) == value);
+      }
+    });
   });
 }