Function added to compute the total envelope of a series of envelopes

• compute_env_of_env function added: it can compute a total envelope for a series of single simulations or a general cloud of points;
• int_envelope function moved out of Cases class;
• proj_envelope function added: it projects the envelope at given angles of a polar coordinates system and translate back to cartesian coordinate;
• compute_envelope function modified to accomadate changes genarate by moving inte_envelope out of Cases class;
• bug fixes.