Merge branch 'feature/fix-gmres-and-minres'

* feature/fix-gmres-and-minres:
  [GMRes] Fix deprecation warning for old constructors
  made the distinction between field_type and real_type which is the same for real numbers but differs for std::complex
  added the old constructors called with the variable recalc_defect to RestartedGMResSolver and set them as deprecated, since they should not be used anymore
  changed the initialization of the arrays in the MinRes solver to remove the compiler warnings
  fixed MinRes with the following changes:
  fixed GMRes

Conflicts:
	dune/istl/solvers.hh