- Required lib version can be in a range
- conan build ../path/to/source builds with conan specified compiler

Cleanup output messages

The time for the linear solver is written already in NonLinearSolver::solver().

Update CTests

Add NOT OGS_USE_MPI to explicit requirements for the non-mpi tests.
For the parallel tests require mpi.

Fluid density model based on IAPWS Industrial Formulation 1997

[FL] Removed mutable type specifier

[FL] Simplified some calculations and changed the documentation

according to Dima's comments.

[FL] Corrected a documentation for an argument of the member of getdValue

[Jenkins] Build is marked as unstable if there is any Doxygen warning

[FL] Fixed two compilation warnings in WaterViscosityIAPWS.cpp

IAPWS viscosity model of water