Fix/settings bugs and added model SettingKeyType typing (#4944)

* fix .gitignore and spelling issues

* Fix setting get not cached correctly

* Add model to settings key type

* Fix plugin setting slug url

* Fix typo

* Fix resetting of related setting field

* Improved model comment

.gitignore

@@ -97,7 +97,7 @@ node_modules/
 maintenance_mode_state.txt
 
 # plugin dev directory
-./plugins/
+InvenTree/plugins/
 
 # Compiled translation files
 *.mo