Change vtkDaxMarchingCubes to vtkDaxContour

We want our filter to behave more like the more modern vtkContourFilter
than the old vtkMarchingCubes. Besides, we would like our Dax filter to
handle contouring in cells other than just cubes.

Change-Id: Ic18b1570835797ed042da626ef8364def96e08b5
Add compute scalars to Dax contour filter.

The Dax contour filter can now interpolate the values of point fields so
that the output will have field information.

Change-Id: I9bd71d05ce255054d2e5d0390577828c64def259
Support Dax marching tetrahedra

Embedded in vtkDaxContour algorithm. Automatically switches to marching
tetrahedra when doing contour on unstructured grid made up of only
tetrahedra.

Change-Id: Ia3cca64666b1c246203b55fbb6b3ec3b5ea0ad5d
Support passing point field data in Dax threshold filter.

Change-Id: Id4bbf39ead9e18972e831f7323c8369b1bb08e80
Merge topic 'improve-dax-contour' into master

93c30ce4 Support passing point field data in Dax threshold filter.
95a86c59 Support Dax marching tetrahedra
423e2485 Add compute scalars to Dax contour filter.
93a1db37 Change vtkDaxMarchingCubes to vtkDaxContour