Updates design to match new `osu-web` design. Adds TestCase for visual testing.
# Conflicts: # osu.Game.Tests/Visual/TestCaseChatLink.cs
-don't directly set AllowOverlay Bindable this should be done specifically where needed -remove AllowOverlay Bindable from ButtonSystem -remove unnecessary xmldoc
+ fix Toolbar being toggleable when it shouldn't be able to + allow opening overlays in MenuState.Initial again
# Conflicts: # osu.Game/Overlays/Music/PlaylistOverlay.cs # osu.Game/Screens/OsuScreen.cs