BUG #13999. Fix OpenDataFile().

Adding new vtkSMCoreUtilities class that can consolidate miscellaneous utility
methods. Added a method to vtkSMCoreUtilities to locate the "file-name"
property. Making the UI and Python use the same method to locate the file-name
property. This addresses the issue when ImageReader was created to open a *.raw
file.

Change-Id: I700ea9aad2b6e393231a9c6f3e81ebce7b22e36a
Merge topic '13999_fix_open_datafile' into next

b94a404 BUG #13999. Fix OpenDataFile().