The `Register()` function can now handle error results and the error will be passed immediately to the Qt frontend, instead of being ignored silently and failing later with a "Room is not registered".
Based on the `roles` payload in the JWT, the rooms will now give mod permission to Citra Community Moderators. To notify the client of its permissions, a new response, IdJoinSuccessAsMod is added, and there's now a new RoomMember::State called Moderator.
Displayed username along with nickname (when they are not identical); Requested and displayed user's avatar; Made the dialog bigger for extended names.
Added a few functions to web_backend (GetImage, GetPlain) to support getting data in multiple content-types.
Added a no_avatar icon for users without avatars.
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.
