ENH: New color rescale based on visible data

Change-Id: Idbf484757c565729656bb8dc8fd87b8359fb38e3
Make vtkExtractSelectionRange work in parallel.

Also cleaned up code: using macros when applicable and removing
unnecessary overloads.

Change-Id: I2b7941f822a3d00f92348ff3f7eef0f93ccb747b
Update icon for reset-to-visible-range.

Change-Id: I14e71b960e98f800e6eb08f153701e6b9399ebd1
Minor code restructuring for consistency.

Moving the method to rescalate LUT to visible range to
vtkSMPVRepresentationProxy from vtkSMTransferFunctionProxy.

Moving ExtractSelectionRange to "internal_filters".

Change-Id: I6a734d20b146497ba74e59e8875ec3db19316b77
Adding test to test resetting to visible range.

Change-Id: Ib4ec7037fe8d894805db33c0dddaeb3a69956d7e
Merge topic 'visible_range' into next

c75260f9 Adding test to test resetting to visible range.
bc34cbc2 Minor code restructuring for consistency.
52367802 Update icon for reset-to-visible-range.
90269fc4 Make vtkExtractSelectionRange work in parallel.
5d36f761 ENH: New color rescale based on visible data