Jacobi-matrix calculation via new Kernel helper class!

phasemapper: added Kernel helper class with methods to calculate the jacobi
matrix or to multiply a vector with the (transposed) jacobi matrix without
explicitly calculating the full matrix
magcreator: added Shape.ellipsoid
numcore: added (experimental) speed-up for jacobi-matrix (not faster)
scripts: modified get_jacobi to test the new Kernel class,
tests: test_compliance now also searches and creates a list of TODOs