Feature/organize traits

I'd like to keep things organized before they get out of hand.

This puts the traits structs to a dedicated namespace Traits, but leaves the traits utilities in the namespace Dune::MatrixVector. It makes use of the traits utilities in several places (axpy, axy, transformmatrix), which IMHO improves readability a lot. Adds deprecation warnings for the moved files.

Additionally this extend traits that the core modules are lacking, e.g. FieldTraits for ScaledIdentityMatrix.

dune/matrix-vector/test/resizetest.cc

@@ -17,7 +17,6 @@
 #include <dune/matrix-vector/algorithm.hh>
 #include <dune/matrix-vector/resize.hh>
 
-
 /// custom multitype types to allow for BlockVector nesting
 template <class... Args>
 struct CustomMultiTypeBlockVector : public Dune::MultiTypeBlockVector<Args...> {
@@ -28,19 +27,19 @@ struct CustomMultiTypeBlockMatrix : public Dune::MultiTypeBlockMatrix<Args...> {
   constexpr static int blocklevel = 1; // fake value
 };
 // inject matrix traits for CustomMultiTypeBlockMatrix
-namespace Dune { namespace MatrixVector {
+namespace Dune { namespace MatrixVector { namespace Traits {
   template <class... Args>
   struct MatrixTraits<CustomMultiTypeBlockMatrix<Args...>> {
     constexpr static bool isMatrix = true;
   };
-}}
+}}}
 // inject vector identification trait for CustomMultiTypeBlockVector
-namespace Dune { namespace MatrixVector {
+namespace Dune { namespace MatrixVector { namespace Traits {
   template <class... Args>
   struct VectorTraits<CustomMultiTypeBlockVector<Args...>> {
     constexpr static bool isVector = true;
   };
-}}
+}}}
 
 
 class ResizeTestSuite {