Make parameters names consistent

[matteobecchi]

There are parameters that have different names in different functions, for instance "n_cores" vs "num_processes", or "selection" vs "centers" and so on.
Make everything consistent across all modules.

[matteobecchi]

trajectory.Trj()

• .get_coordinates(): selection ✅
• .get_coord_number(): r_cut, n_jobs, selection. Missing “target”.
• .get_lens(): r_cut, delay, selection, n_jobs. Missing “target”.
• .get_soap(): r_cut, selection, centers, respect_pbc, n_jobs. Make names consistent with the rest.
• .get_orientational_op(): r_cut, selection, n_jobs. Missing “target”?
• .get_velocity_alignment(): r_cut, selection, n_jobs. ✅

trajectory.Insight()

• .spatial_average(): r_cut, selection, n_jobs. ✅
• .get_angular_velocity(): delay. ✅

lens

• list_neighbours_along_trajectory(): universe, r_cut, selection, n_jobs. Missing “target”.
• neighbour_change_in_time(): delay. Missing “target”.

timesoap

• normalize_soap(): soap. ✅
• timesoap(): delay, soap. ✅

analysis

• spatialaverage(): selection, r_cut, n_jobs. ✅