sort dlc filenames when reading into list of cases to avoid random order

the random order was causing a crash in our OpenMDAO wrapper since individual nodes were reading in cases in random order.

See merge request !12

prepost.Simulations: errorlog indicates number of errors, not all line nr occurances (can be too many)

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

Conflicts:
	wetb/prepost/Simulations.py

set to pbs_in_turb, fix tests

Added interpolation envelope function in "Simulations"

A new function "int_envelope" is added in Simulations to interpolate linearly the closed contours from the convex hulls in a defined amount of points (default set Nx=300).

New additions:
- "int_envelope" function;
- flag "int_env"(set as False) in the "compute_envelope" function; if the flag is set as True, the computed evelope is interpolated in a given set of points. 

See merge request !8

pbs_in_failed, silent switches for printing
create pbs_in files for Mann64 turbulence generator

- number of interpolation points added to "compute_envelopes"