Add range slider widgets from ctk

This adds both double and integer double-ended range slider from the
common toolkit CTK (https://github.com/commontk/CTK).

The versions of files imported from CTK come from CTK
revision. 71c756a32052f1f04cf10b111a18826e95347d34

The changes made to the headers include removing CTK headers that were
unused and updating the export macro for the appropriate paraview
library.  Additionally the paraview license was prepended.

Change-Id: I53fe3c13c8bddeb1551423d4eda422a3bea5072f
Basic test for CTK range sliders

This test does not verification of the code as that is assumed to be
tested in CTK.  Instead this provides a simple example that can be run
to illustrate the use of the two widgets.

Change-Id: I96d934429331e3328d728cdb793ccc48441d601e
Merge topic 'double_slider' into next

199bca5 Basic test for CTK range sliders
4d8bb08 Add range slider widgets from ctk