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

Port 913a38111f to glitch-soc

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

@@ -0,0 +1,18 @@
+import Immutable from 'immutable';
+import {
+  DROPDOWN_MENU_OPEN,
+  DROPDOWN_MENU_CLOSE,
+} from '../actions/dropdown_menu';
+
+const initialState = Immutable.Map({ openId: null, placement: null });
+
+export default function dropdownMenu(state = initialState, action) {
+  switch (action.type) {
+  case DROPDOWN_MENU_OPEN:
+    return state.merge({ openId: action.id, placement: action.placement });
+  case DROPDOWN_MENU_CLOSE:
+    return state.get('openId') === action.id ? state.set('openId', null) : state;
+  default:
+    return state;
+  }
+}