Initialize config with the default settings

src/lib/MiradorViewer.js

 import React from 'react';
 import ReactDOM from 'react-dom';
 import { Provider } from 'react-redux';
-import deepmerge from 'deepmerge';
 import uuid from 'uuid/v4';
 import PluginProvider from '../extend/PluginProvider';
 import App from '../containers/App';
 import createStore from '../state/createStore';
 import createRootReducer from '../state/reducers/rootReducer';
 import * as actions from '../state/actions';
-import settings from '../config/settings';
 import { getCompanionWindowIdsForPosition, getManifestSearchService } from '../state/selectors';
 
 /**
@@ -43,12 +41,11 @@ class MiradorViewer {
    */
   processConfig() {
     /** merge type for arrays */
-    const overwriteMerge = (destinationArray, sourceArray, options) => sourceArray;
-    const mergedConfig = deepmerge(settings, this.config, { arrayMerge: overwriteMerge });
-    const action = actions.setConfig(mergedConfig);
+    const action = actions.importConfig(this.config);
     this.store.dispatch(action);
+    const { config: storedConfig } = this.store.getState();
 
-    mergedConfig.windows.forEach((miradorWindow, layoutOrder) => {
+    storedConfig.windows.forEach((miradorWindow, layoutOrder) => {
       const windowId = `window-${uuid()}`;
       const manifestId = miradorWindow.manifestId || miradorWindow.loadedManifest;
       const manifestAction = this.store.dispatch(actions.fetchManifest(manifestId));
@@ -57,7 +54,7 @@ class MiradorViewer {
         id: windowId,
         layoutOrder,
         manifestId,
-        thumbnailNavigationPosition: mergedConfig.thumbnailNavigation.defaultPosition,
+        thumbnailNavigationPosition: storedConfig.thumbnailNavigation.defaultPosition,
         // ... overridden by values from the window configuration ...
         ...miradorWindow,
       }));
@@ -81,9 +78,9 @@ class MiradorViewer {
       });
     });
 
-    Object.keys(mergedConfig.manifests || {}).forEach((manifestId) => {
+    Object.keys(storedConfig.manifests || {}).forEach((manifestId) => {
       this.store.dispatch(
-        actions.requestManifest(manifestId, mergedConfig.manifests[manifestId]),
+        actions.requestManifest(manifestId, storedConfig.manifests[manifestId]),
       );
     });
   }

src/state/reducers/config.js

 import deepmerge from 'deepmerge';
+import settings from '../../config/settings';
 import ActionTypes from '../actions/action-types';
 
+const initialState = { ...settings };
+
+/** Overwrite arrays when deep merging */
+const overwriteMerge = (destinationArray, sourceArray, options) => sourceArray;
+
 /**
  * configReducer - does a deep merge of the config
  */
-export const configReducer = (state = {}, action) => {
+export const configReducer = (state = initialState, action) => {
   switch (action.type) {
     case ActionTypes.UPDATE_CONFIG:
     case ActionTypes.IMPORT_CONFIG:
-      return deepmerge(state, action.config);
+      return deepmerge(state, action.config, { arrayMerge: overwriteMerge });
     case ActionTypes.SET_CONFIG:
       return action.config;
     case ActionTypes.IMPORT_MIRADOR_STATE: