Move triangle decomposition to inpgen
In a film calculation decompose the kpoint set into triangles in the inpgen and write it to the kpts.xml analogously to the tetrahedrons
Why is this feature needed?
First of all it's much nicer if the bulk and film case do not differ massively. Second it would be useful if this information would be included in the kpts type for the tetrahedron method I implemented. This is not possible at the moment if triang is called at the fermi energy calculation
We could insert ntria, itria and voltria into the kpt type. Alternatively we could also reuse the arrays for the bulk case as only the ntetra array would differ with 3 instead of 4 k-points in a triangle