Extra parameters (feature from turtle_addons)

This merge request adjusts the use of extra parameters for each simulation type. This should allow to create new simulation types with additional parameters more easily, also by writing classes inheriting from the DNS class.

Please take your time to review this. I tried my best, but of course I cannot ensure that it works as you expect it to in all possible cases.

Note: As far as I can tell, 'static_field_with_ghost_collisions' previously did not have NSVEp_extra_parameters as command line parameters, although I believe it should. I added it in the appropriate place.