Replace random buildings with one using proper instancing.
Also implement more control over rendering of random buildings.
see README.scenery for details.
Add ALS specific vertex shader for ubershader.vert and buildings-ubershader.vert named model-ALS-ultra.vert and buildings-model-ALS-ultra.vert respectively. This partly reverts 3dc0e641c1 . Aircraft modelers and other consumers need not take any action.