Adding brick lintel arches

I am planning to make this Theme have clearly defined social classes to all the buildings.

That'll be organised (hopefully) by wealth-level availability of each growable asset. 

Houses especially will indicate their wealth levels visually by the size per plot, and general filthiness.

I decided, though, for the L1 working class houses that a plastered trapezoid lintel was far far too posh, and modelled these brick arch lintels instead.