SMTK requires C++11 but doesn't enable C++11 when building.

SMTK now requires C++11 to be enabled, since the polygon bridge uses std::list api that are only in C++11 ( erase( const_iter) )

In our CMake code we need to explicitly state that we need to be built with the proper compile flags to enable C++11. This should be done by using CMake CMAKE_CXX_STANDARD and CMAKE_CXX_STANDARD_REQUIRED properties.