Warn of unused variables in C++ code

Warn of unused variables in C++ code

- Replace -Wunused by -Wunused-function for C++
- Remove all unused variables in C++
- Replaced static const in headers used by C++ by get function for constant
- Also warn of non-virtual-dtor and sign-compare
- Removes src/contrib/copyrgt.c. Is not needed anymore for manual.
  If it is needed for other purposes should be rewritten using CopyRight(...)
  (from src/gromacs/legacyheaders/copyrite.h)

Change-Id: I9046eae5d097e65607add7a18a3a7e8c643c8331