Re-implements chat sync and clear

...button-html5/imports/api/group-chat-msg/server/methods.js

...p-chat-msg/server/methods/chatMessageBeforeJoinCounter.js

.../api/group-chat-msg/server/methods/fetchMessagePerPage.js

...ton-html5/imports/api/group-chat-msg/server/publishers.js

bigbluebutton-html5/imports/ui/components/chat/component.jsx

bigbluebutton-html5/imports/ui/components/chat/container.jsx

...imports/ui/components/chat/time-window-list/component.jsx

...ts/ui/components/components-data/chat-context/adapter.jsx

...ts/ui/components/components-data/chat-context/context.jsx

bigbluebutton-html5/private/config/settings.yml

bigbluebutton-html5/private/locales/en.json