Route screen size queries via Game.Renderer.
Tidy WorldCommandWidget.
Route viewport centering via WorldRenderer.
Move more viewport lookups to WorldRenderer.
Add ScreenMap.ActorsAt(MouseInput) overload.
Remove WorldUtils.FindFrozenActorsAtMouse.
Add Game.Zoom for remaining engine stuff.
Move Viewport inside WorldRenderer.
Clean up viewport internals.
Merge pull request #3887 from pchote/viewport-cleanup

Viewport cleanup