Streamline how temp directories are created

[andreaslundell]

• Refactored the code to create temporary directories to the Utilities-class.
• Used this functionality in Solver.cpp (two places) and ModelingSystemGAMS.cpp`.
• Logic:
  • If the debug mode is not activated no debug directory is obviously created. A GAMS temporary directory is created as /tmp/SHOT_GAMS_*****/. This directory is deleted when SHOT exits.
  • If the debug mode is activated but the debug directory is not specified, a directory /tmp/SHOT_debug_*****/ is used. In this directory a directory SHOT_GAMS_**** is created where the GAMS temporary files are put. These directories are not removed on exit.

This works well when using SHOT directly on a GAMS problem file, but does it work when called from GAMS (espcially after https://github.com/coin-or/SHOT/commit/06e768279fec30b796737a013993b36ecb7c8843)?

[svigerske]

I took 06e7682 back again. The new one with the tempdir is nicer, since the gams scratch dir is deleted by default.