vtkPythonCommand - Add support for additional call data types

This commit extend the mechanism added in 9366ca67 to support additional
data types.

Supported types now includes 'string0', 'vtkobject', 'int', 'long',
'double' and 'float'.

Also added
 (1) convenience decorator 'set_call_data_type'
 (2) test checking CallDataType can be associated with observer callback

See inlined comments for more details.

Change-Id: I8b27ccca63b9a5a30e7a0cedda2b789f8f66e0e5
vtkPythonCommand - Fix indent and variable names

Change-Id: I7683ccf508906d3facd7e618eaaa5140e2d87c99
ENH: Enable selection of translucent geometry

vtkHardwareSelector was skipping all translucent geometry and selecting only
opaque geometry. This change enables selection of translucent as well as opaque
geometry. Totally transparent (opacity = 0.0) is skipped.
This change fixes ParaView issue 14412

Change-Id: Ic8ead1534b4f24695e5138fc8207250f25450508
Merge topic '14581-volume-render-bug' into pv-master

a43fb6ae Don't reset traversal location in each iteration of box clip filter.
Merge remote-tracking branch 'pvvtk/pv-master' into HEAD

* pvvtk/pv-master:

Change-Id: I1a00dc35822f8a50be7081040b985609f8120ac0
Merge topic 'python-command-support-additional-call-data-types' into master

176861d8 vtkPythonCommand - Fix indent and variable names
50d601bd vtkPythonCommand - Add support for additional call data types
Merge topic 'select-translucent-geometry' into master

4724a470 ENH: Enable selection of translucent geometry