FIX: Fix Model's scalar selection

Following CTK's commit to fix the vtk dataset model, we can now
appropriately select a cell data array and have it displayed correctly.

MISSING EXTERNAL_CTK UPDATE !!!
HACK: Use lookup table range for model scalar array display

The following missing feature http://na-mic.org/Mantis/view.php?id=3573
prevents us from displaying the tetrahedral mesh correctly.
While waiting for a fix, we hack the displayable manager to prevent the
scaling of the lookup table to the data.

THIS COMMIT SHOULD NOT BE MERGED IN SLICER !