Add scaling options

[csherratt]

The primitives right now just produce a primitive that is close to a unit vector. The original idea was that people would scale the primitives using the .vertex() trait. There are a few cases where I don't think this is satisfactory. The cone primitive for example has different normals based on these values, so for the sake of our uses we should add them.

[kvark]

Indeed, the addition of normals makes this point strong. We could also adjust the UVs. E.g. a cube with sizes (5, 1, 1) should have more UV space alongside X axis.