feat(api): notify of password required

doc/api.md

 api.executeCommand('displayName', 'New Nickname');
 ```
 
+* **password** - Sets the password for the room. This command requires one argument - the password name to be set.
+```javascript
+api.executeCommand('password', 'The Password');
+```
+
 * **subject** - Sets the subject of the conference. This command requires one argument - the new subject to be set.
 ```javascript
 api.executeCommand('subject', 'New Conference Subject');
 }
 ```
 
+* **passwordRequired** - event notifications fired when failing to join a room because it has a password.
+
 * **videoConferenceJoined** - event notifications fired when the local user has joined the video conference. The listener will receive an object with the following structure:
 ```javascript
 {

modules/API/API.js

     createApiEvent,
     sendAnalytics
 } from '../../react/features/analytics';
-import { setSubject } from '../../react/features/base/conference';
+import { setPassword, setSubject } from '../../react/features/base/conference';
 import { parseJWTFromURLParams } from '../../react/features/base/jwt';
 import { invite } from '../../react/features/invite';
 import { toggleTileView } from '../../react/features/video-layout';
             sendAnalytics(createApiEvent('display.name.changed'));
             APP.conference.changeLocalDisplayName(displayName);
         },
+        'password': password => {
+            const { conference, passwordRequired }
+                = APP.store.getState()['features/base/conference'];
+
+            if (passwordRequired) {
+                sendAnalytics(createApiEvent('submit.password'));
+
+                APP.store.dispatch(setPassword(
+                    passwordRequired,
+                    passwordRequired.join,
+                    password
+                ));
+            } else {
+                sendAnalytics(createApiEvent('password.changed'));
+
+                APP.store.dispatch(setPassword(
+                    conference,
+                    conference.lock,
+                    password
+                ));
+            }
+        },
         'proxy-connection-event': event => {
             APP.conference.onProxyConnectionEvent(event);
         },
         });
     }
 
+    /**
+     * Notify external application of the current meeting requiring a password
+     * to join.
+     *
+     * @returns {void}
+     */
+    notifyOnPasswordRequired() {
+        this._sendEvent({ name: 'password-required' });
+    }
+
     /**
      * Notify external application (if API is enabled) that the screen sharing
      * has been turned on/off.

modules/API/external/external_api.js

     displayName: 'display-name',
     email: 'email',
     hangup: 'video-hangup',
+    password: 'password',
     subject: 'subject',
     submitFeedback: 'submit-feedback',
     toggleAudio: 'toggle-audio',
     'outgoing-message': 'outgoingMessage',
     'participant-joined': 'participantJoined',
     'participant-left': 'participantLeft',
+    'password-required': 'passwordRequired',
     'proxy-connection-event': 'proxyConnectionEvent',
     'video-ready-to-close': 'readyToClose',
     'video-conference-joined': 'videoConferenceJoined',

react/features/external-api/middleware.js

 // @flow
 
+import { CONFERENCE_FAILED } from '../base/conference';
 import { NOTIFY_CAMERA_ERROR, NOTIFY_MIC_ERROR } from '../base/devices';
+import { JitsiConferenceErrors } from '../base/lib-jitsi-meet';
 import { MiddlewareRegistry } from '../base/redux';
 
 declare var APP: Object;
  */
 MiddlewareRegistry.register((/* store */) => next => action => {
     switch (action.type) {
+    case CONFERENCE_FAILED: {
+        if (action.conference
+            && action.error.name === JitsiConferenceErrors.PASSWORD_REQUIRED) {
+            APP.API.notifyOnPasswordRequired();
+        }
+        break;
+    }
+
     case NOTIFY_CAMERA_ERROR:
         if (action.error) {
             APP.API.notifyOnCameraError(