Variablesbackend does not support Dune::DynamicVector as Dof vector

Bug report The current variablesbackend does not consider the situation that the residual type in assembler in newtonsolver can be DynamicVector.

What happened / Problem description:

 /Applications/DUMUX/dumux/dumux/common/variablesbackend.hh:165:10: error: implicit instantiation of undefined template
      'Dumux::DofBackend<Dune::DynamicVector<double, std::__1::allocator<double> >, false>'
: public DofBackend<Vars>

Environment:

• Dune version:master
• DuMux version:master
• Others:The compiler is clang-1200.0.32.29, operation system is MacOS.