Add new/modified chat report to EWS

Through observation of source code of `itchat`, it seems like Web WC has a mechanism of reporting new/updated chat items. Relevant logic can be found here: https://github.com/blueset/efb-wechat-slave/blob/74b7bd0cf4eab190a0637a496c56849c80c8ecb7/efb_wechat_slave/vendor/itchat/components/login.py#L268-L278

However, seeing the logic is buried deep up the dependency tree, it is hard to expose an interface all the way through to EWS. As this might result in a significant amount of change to these code, I’m considering this as a part of the `async` support for EFB 3 (that may or may not come in the future). If you have any better idea on this, do not hesitate letting us know.