config: add ability to hide the "invite more" header button

interface_config.js

      */
     AUTHENTICATION_ENABLE: true,
 
+    /**
+     * Hide the invite prompt in the header when alone in the meeting.
+     */
+    HIDE_INVITE_MORE_HEADER: false,
+
     /**
      * The name of the toolbar buttons to display in the toolbar. If present,
      * the button will display. Exceptions are "livestreaming" and "recording"

react/features/base/config/interfaceConfigWhitelist.js

     'ENFORCE_NOTIFICATION_AUTO_DISMISS_TIMEOUT',
     'FILM_STRIP_MAX_HEIGHT',
     'GENERATE_ROOMNAMES_ON_WELCOME_PAGE',
+    'HIDE_INVITE_MORE_HEADER',
     'INDICATOR_FONT_SIZES',
     'INITIAL_TOOLBAR_TIMEOUT',
     'INVITATION_POWERED_BY',

react/features/conference/components/web/InviteMore.js

 import { beginAddPeople } from '../../../invite';
 import { isToolboxVisible } from '../../../toolbox';
 
+declare var interfaceConfig: Object;
+
 type Props = {
 
     /**
  */
 function mapStateToProps(state) {
     const participantCount = getParticipantCount(state);
+    const isAlone = participantCount === 1;
+    const hide = interfaceConfig.HIDE_INVITE_MORE_HEADER;
 
     return {
         _tileViewEnabled: state['features/video-layout'].tileViewEnabled,
-        _visible: isToolboxVisible(state) && participantCount === 1
+        _visible: isToolboxVisible(state) && isAlone && !hide
     };
 }