BUG #14270: Fixed external plugins.

When building external plugins that added new modules, we were getting errors
when importing modules defined by ParaView. This was due to a bugs in
pv_setup_module_environment() which resulted in changing the location where the
*.cmake files for the imported modules were searched. Updated
pv_setup_module_environment() to fix that issue and use the
vtkExternalModuleMacros file provided by VTK to simplify the logic.

Change-Id: I8d45c51eea53388bb406f445f2a493185388d894
Add MPI based Web sample application

The ParallelViz Web application provide an example
on how to setup a ParaViewWeb application for Parallel visualization.

The default example use a dummy sphere source colored by process id.

Change-Id: I0cf60b9fcebcf51d8cd69b222f24301fffd0c52c
Load Native Python module instead of Python indirection

Change-Id: Ie0c26996939c577d428d9c8e66895daed184e7f3
Merge topic 'add-parallel-web-demo'

8027621 Add MPI based Web sample application
Merge topic 'fix-coprocessing-script'

7469a1d Load Native Python module instead of Python indirection
Merge topic 'fix_external_plugins'

5c3c9d9 BUG #14270: Fixed external plugins.