add support for vectorization library VC

This branch adds support for the Vc library, which add support for vectorization, including an abstraction for intrisics.

We have been using in EXA-Dune and I belive that the integration of vectorization support into the core-Dune is something Dune in general can benefit from. A separate branch I'm preparing for ISTL will add support for multiple RHS vectors using vectorization.

The branch collects a set of helper classes which allow to add vectorization support to your code with moderate effort. Mainly this means that we have a couple of utility functions, which work for scalar data types, ranges and SIMD data types alike.

doc/doxygen/modules.txt

@@ -21,6 +21,15 @@
   @ingroup Utilities
 */
 
+/**
+ @defgroup RangeUtilities Range Utilities
+ @brief Utilities for reduction like operations on ranges
+
+ All these reduction operations work for appropriate ranges and scalar values
+
+ @ingroup Utilities
+*/
+
 /**
   @defgroup StringUtilities String Utilities
   @brief Utility functions for std::string