New algorithm for rendering the cube caps.
The caps are now made up of many small triangles.

This is needed so that we can have caps on the upcoming sphere effect.

Also this way it is possible to paint textured cap in one step and not in two.
So the opacity of the textured caps is now correct.
The texture has got a border of one pixel in cap color so that the texture can be used to paint the whole cap and transparent areas of the texture are manually blended with the cap color.