Some refactoring to be done #60
Description
linear_normal_form.py should be moved to xpart.
Methods find_closed_orbit_from_tracker and compute_R_matrix_finite_differences could go to xtrack
Check det(R) == 1 and symplectification should go in compute_linear_normal_form
_set_orbit_dependent_parameters_for_bb ported to xfields, should be removed from pymask. NB: function from xsuite does not re-enable the bb lenses, this needs still to be done by pymask (explicitly)
I would like to remove check against sixtrack from xline example, can use paymaster test for this. Needs to be extended with ebe functionalities.