[Glitch] Remove pointer events on the entire UI when a dropdown menu is open

Port 913a38111f to glitch-soc

app/javascript/flavours/glitch/reducers/index.js

@@ -1,4 +1,5 @@
 import { combineReducers } from 'redux-immutable';
+import dropdown_menu from './dropdown_menu';
 import timelines from './timelines';
 import meta from './meta';
 import alerts from './alerts';
@@ -27,6 +28,7 @@ import lists from './lists';
 import listEditor from './list_editor';
 
 const reducers = {
+  dropdown_menu,
   timelines,
   meta,
   alerts,