Dax marching cubes now uses input array not active scalars.

The superclass still has the problem of only getting the active
scalars rather than the input array. It would be good if this were
fixed. It might be even better if vtkDaxMarchingCubes inherited from
vtkContour instead. This class both handles the input array correctly
and has better implementations of the contour algorithm.

Change-Id: Iac333cb5019b28f7fb4bf2fb62e28b898593491f
Allow Dax marching cubes and threshold to work with doubles.

Change-Id: I289624b773f148eb530e58c745f4150297e20170
Merge topic 'dax_updates' into master

c5333aac Allow Dax marching cubes and threshold to work with doubles.
c29aa732 Dax marching cubes now uses input array not active scalars.