All templated code has been consolidated into a single templated
class. The vtkSMPTools::For() has been rewritten to loop over slices
rather than edges (a tad faster and the code is cleaner).

Trying different looping strategies.

Each of the three passes of the algorithm has been integrated
into the vtkSMPTools. This enables TBB and X-Kaapi support (as
well as well as sequential and simple vtkMultiThreader
capabilities). Note that there is no distinction between a serial
and parallel version of FlyingEdges (i.e., separate implementations).