The user would be notified if the message contains "@" followed by the user's nickname or forum username. An alert would be shown, and the icon and message in the status bar would be changed. All notification is only shown if the chat window currently does not have focus.
Also added a connected_notification icon for showing in the status bar.
To allow for passing moderation errors around without impacting the State, this commit also separates the previous State enum into two enums: State, and Error. The State enum now only contains generic states like disconnected or connected, and the Error enum describes the specific error happened.
citra_qt/multiplayer/{state, message} is changed accordingly.
In dark theme, it is very hard to see the connected/disconnected icons because they are dark too. So I added two white-coloured icons for the dark theme. This also fixed an issue where theme update does not change the icon on the status bar.
