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.

See merge request !11