The multiplayer state object and dialogs hold a (modified) game list model, but it isn't updated when the actual game list changes. This updates the multiplayer dialogs with the new game list when it got repopulated.
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.
