* input/regression/tie-chord.ly: use generateTiePattern to

* input/regression/tie-chord.ly: use generateTiePattern to
simplify file.

* lily/tie-formatting-problem.cc (peak_around): new function.
(score_configuration): use sliding criterion for staff line collisions.
(score_configuration): idem for dot collisions.
(generate_configuration): use separate stem_gap for gap to stem.

* lily/include/tie-formatting-problem.hh (struct Tie_details):
separate penalty factors for x and y distance.
(struct Tie_details): separate penalties for tip and center line collisions.