#48: Support pinning files to cache [partial]

src/redux/reducers/pinned_manager_reducer.js

@@ -0,0 +1,13 @@
+import {createReducer} from '@reduxjs/toolkit';
+import {displayPinnedManager} from '../actions/pinned_manager_actions';
+
+export const pinnedManagerReducer = createReducer({
+  DisplayPinnedManager: false,
+}, {
+  [displayPinnedManager]: (state, action) => {
+    return {
+      ...state,
+      DisplayPinnedManager: action.payload,
+    };
+  },
+});