Merge branch 'correct_vtkm_pair_init' into 'master'
Properly initialize vtkm::Pair, and remove the TypeTrait for it. vtkm::Pair can hold vtkm::Vec so we need to call the proper constructor for vtkm::Vec. Now that vtkm::TypeTraits don't error out on unknown types, we don't need the weird specialization for vtkm::Pair. See merge request !39