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.
* Move Joining state change sooner in the code to prevent an issue where
failing to connect multiple times in a row doesn't change the state (as
it goes from CouldNotConnect -> CouldNotConnect which doesn't trigger a
state changed callback)
* Prevent double clicking too fast on a room in the lobby from causing
issues
* Lobby no longer closes when joining a room
Each window can still watch for state changes to update the ui or to
close the window as appropriate, but for any error announcements, they
all belong in Multiplayer state now.
