Fix for cases when the coordinate types in the file do not match
vtkm::FloatDefault. This resulted in bad dynamic cast exceptions.

Worklets should never set or define the default device adapter

Most uses of this macro appeared before any associated `template` lines.
Make them consistent. This also makes clang-format happier.

This has been done to reduce memory overhead; as we don't need to store
normals for all points before finding the unique subset, and also improving
performance of the algorithm.

Performance numbers on dataset of (863, 863, 863):

Original version(TBB): 13.03974sec
New version(TBB): 11.79939sec

Previously when you permuted a structured cellset you would get a permuted
point coordinates. This would cause the Cell operations to take non
optimal paths.

add read only (for the moment) test and implementation of ArrayHandleReverse (a.k.a reverse iterator)