Background: shrink background surface

[pkulev]

Abstract

Background tries to render on border (I've learned it from renderer logs).
This is not quite good because:

• Border is for GUI only, rendering other things on it breaks look.
• Renderer doesn't render Backgound on border, but sends remove_obsolete signal almost every frame.

Implementation

Find place where Surface sends to renderer and don't use (x, 0) and (x, Settings.layout.border.y) coordinates.