add Thermostatic3WayValvePI.mo
solved issue where thermostatic3WayValve had a division by zero when the two incoming enthalpies are equal
Merge branch 'issue111_3wayValve' of github.com:open-ideas/IDEAS into issue111_3wayValve

it merges an updated upstream into a topic branch.
reduce PI gain in valve to make the system more stable.
Merge branch 'issue111_3wayValve' of https://github.com/open-ideas/IDEAS into CrashCourse

Conflicts:
	IDEAS/Fluid/Valves/Thermostatic3WayValve.mo
	IDEAS/Fluid/Valves/Thermostatic3WayValvePI.mo
change Thermostatic3WayValve to new implentation of Filip.