Reorganize Trajectories methods (no API changes)
Trajectories: new colors method (no API changes) and tests
Trajectories: fix bug in t_stamp() and labels(), not updated when labels or t_stamp was removed
Trajectories: fix relabel_fromzero() and add more tests
Trajectories: rename merge_label_safe to merge (old method still available but raise a warning
Trajectories: add remove_spots and test
Trajectories: add default  parameter to  in relabel_fromzero
Trajectories: add merge_segments and test
Trajectories: add cut_segments and duplicate_segments. Various small fixes and still more tests (Trajectories has 100% coverage).
Trajectories: small bug fixes because returning pd.DataFrame instead of Trajectories