feat(config): Add config option to allow unsetting local video flip

config.js

     // the menu has option to flip the locally seen video for local presentations
     // disableLocalVideoFlip: false,
 
+    // A property used to unset the default flip state of the local video.
+    // When it is set to 'true', the local(self) video will not be mirrored anymore.
+    // doNotFlipLocalVideo: false,
+
     // Mainly privacy related settings
 
     // Disables all invite functions from the app (share, invite, dial out...etc)

react/features/base/config/configWhitelist.js

     'disableTileView',
     'displayJids',
     'doNotStoreRoom',
+    'doNotFlipLocalVideo',
     'dropbox',
     'e2eping',
     'enableDisplayNameInStats',

react/features/base/config/middleware.js

 import { getFeatureFlag } from '../flags/functions';
 import { addKnownDomains } from '../known-domains';
 import { MiddlewareRegistry } from '../redux';
+import { updateSettings } from '../settings';
 import { parseURIString } from '../util';
 
-import { SET_CONFIG } from './actionTypes';
+import { SET_CONFIG, OVERWRITE_CONFIG } from './actionTypes';
 import { updateConfig } from './actions';
 import { _CONFIG_STORE_PREFIX } from './constants';
 
 
     case SET_CONFIG:
         return _setConfig(store, next, action);
+
+    case OVERWRITE_CONFIG:
+        return _updateSettings(store, next, action);
     }
 
     return next(action);
         config.resolution = resolutionFlag;
     }
 
+    if (action.config.doNotFlipLocalVideo === true) {
+        dispatch(updateSettings({
+            localFlipX: false
+        }));
+    }
+
     dispatch(updateConfig(config));
 
     // FIXME On Web we rely on the global 'config' variable which gets altered
 
     return result;
 }
+
+/**
+ * Updates settings based on some config values.
+ *
+ * @param {Store} store - The redux store in which the specified {@code action}
+ * is being dispatched.
+ * @param {Dispatch} next - The redux {@code dispatch} function to dispatch the
+ * specified {@code action} in the specified {@code store}.
+ * @param {Action} action - The redux action which is being {@code dispatch}ed
+ * in the specified {@code store}.
+ * @private
+ * @returns {*} The return value of {@code next(action)}.
+ */
+function _updateSettings({ dispatch }, next, action) {
+    const { config: { doNotFlipLocalVideo } } = action;
+
+    if (doNotFlipLocalVideo === true) {
+        dispatch(updateSettings({
+            localFlipX: false
+        }));
+    }
+
+    return next(action);
+}