add elementary implementation of all different constraint
add elementary implementation of all different constraint

the idea is to have a more interesting example than tsp and
also to have a more complicated constraint to test.
However is not complicated enough so it doesn't get copied,
transformed, etc.

mattmilten/PySCIPOpt,SCIP-Interfaces/PySCIPOpt,mattmilten/PySCIPOpt,SCIP-Interfaces/PySCIPOpt