Fix ParaViewWeb iPython module

Previously the iPython module was making the
python interpreter crash when ran with MPI.
The reason was the import paraview.simple
before any valid MPI initialization.
Further fix have also be made along a documentation

Change-Id: Ibd2c388ed1aef453f9aa3e1cf3250582a1819099
Merge topic 'pvweb-ipython-integration' into next

577167c Fix ParaViewWeb iPython module