WIP add bulk insert and throttle for chat messages

...-html5/imports/api/group-chat-msg/server/eventHandlers.js

...i/group-chat-msg/server/handlers/groupChatMsgBroadcast.js

...orts/api/group-chat-msg/server/handlers/syncGroupsChat.js

...i/group-chat-msg/server/modifiers/addBulkGroupChatMsgs.js

...ts/api/group-chat-msg/server/modifiers/addGroupChatMsg.js

bigbluebutton-html5/private/config/settings.yml