- Get rid of the derivation from Triangulation_3
  add a Triangulation_3 as a data member 
  creators from a triangulation:
  Alpha_shape_3(cnst Dt& dt, NT alpha = 0, Mode m = REGULARIZED)
  The triangulation is copied
  Alpha_shape_3(Dt& dt, bool swap=true, NT alpha = 0, Mode m = REGULARIZED)
  The triangulation is swapped  if swap=true and copied otherwise.

- suppress the traits classes Alpha_shape_euclidean_traits_3.h
  and Weighted_alpha_shape_euclidean_traits_3.h
  their purpose was to rename the Compute_squared_radius_3 constructor.
  The same can be achieved in class Alpha_shapes_3 using the Weighted_tag
  of the triangulation

- same as previous for Alpha_shapes_2

- test the  taking into account of paramater alpha in functions
get_alpha_shape_edges
get_alpha_shape_facets
get_alpha_shape_vertices
get_alpha_shape_cells