Api (#2439)

* [Update] 迁移settings到独立app

* [Update] 修改settings migrations

* [Update] 修改docs说明

apps/settings/apps.py

@@ -0,0 +1,8 @@
+from django.apps import AppConfig
+
+
+class SettingsConfig(AppConfig):
+    name = 'settings'
+
+    def ready(self):
+        from . import signals_handler