heat-exchanger OpenFOAM is missing run.sh

[MakisH]

https://github.com/precice/tutorials/tree/develop/heat-exchanger

Previous Allrun: https://github.com/precice/tutorials/blob/master/CHT/heat_exchanger/buoyantSimpleFoam-CalculiX/Allrun

It also specifies CalculiX v2.12 in the README, which we should remove.

[MakisH]

Implemented in #181.