* started chat model * refactor processing commands and UI events * message chat event processing * groups: delayed delivery of messages and introductions to announced members (#217) * combine migrations, rename fields * show all view messages vis ChatResponse type * serialize chat response * update C api * remove unused extensions, fix typos Co-authored-by: Efim Poberezkin <8711996+efim-poberezkin@users.noreply.github.com>