feat(external-api): Add send chat message command

modules/API/API.js

 import { updateSettings } from '../../react/features/base/settings';
 import { isToggleCameraEnabled, toggleCamera } from '../../react/features/base/tracks';
 import {
+    sendMessage,
     setPrivateMessageRecipient,
     toggleChat
 } from '../../react/features/chat/actions';
             sendAnalytics(createApiEvent('avatar.url.changed'));
             APP.conference.changeLocalAvatarUrl(avatarUrl);
         },
+        'send-chat-message': (message, to, ignorePrivacy = false) => {
+            logger.debug('Send chat message command received');
+            if (to) {
+                const participant = getParticipantById(APP.store.getState(), to);
+
+                if (participant) {
+                    APP.store.dispatch(setPrivateMessageRecipient(participant));
+                } else {
+                    logger.error(`Participant with id ${to} not found!`);
+
+                    return;
+                }
+            } else {
+                APP.store.dispatch(setPrivateMessageRecipient());
+            }
+
+            APP.store.dispatch(sendMessage(message, ignorePrivacy));
+        },
         'send-endpoint-text-message': (to, text) => {
             logger.debug('Send endpoint message command received');
             try {

modules/API/external/external_api.js

     password: 'password',
     pinParticipant: 'pin-participant',
     resizeLargeVideo: 'resize-large-video',
+    sendChatMessage: 'send-chat-message',
     sendEndpointTextMessage: 'send-endpoint-text-message',
     sendTones: 'send-tones',
     setLargeVideoParticipant: 'set-large-video-participant',