Vectorization (SIMD) of Vector

Use OpenMP to vectorize some operations in Vector. The class is a little bit messier now because I cannot use lambda function with OpenMP. 
It is set in any case, but it is 0 on systems that do not support SSE2; similar construct as in base/aligned_vector.h and base/vectorization.h, and set in cmake/checks/check_01_cpu_features.cmake.