Moved `PluginsManager` and `PluginsManagerType` from `servers::plugin::manager` to the `servers::plugin` module.
Added some comments in code.
Implemented function `into()` to the `PluginsManager` struct.
- Better Client struct (TCP and WebSocket in one type)
- WebSocket is now not a proxy to tcp
- Use async-std instead a tokio
- Use Arc and Client type now have a Clone derive
- Add global CLIENTS list
- added `/disconnect` commands
- moved logger init function to other file
- updated command description
- the `/help` command has been accelerated
- re-export `async_trait` so that it doesn't have to be added to dependencies in plugins