/**
 * This method activates the given channels for username and room.
 *
 * By passing an empty array as channels the notification is turned off.
 *
 * @param usernames - the users to notify 
 * @param roomId - the id of the room the users should be notified about
 * @param channels - channels (desktop, mobile, email) to activate for notification
 */
createNotifications = function(usernames, roomId, channels[]);