Added module registration api to vtkWeb, also added registration.

In vtkWeb object there is now a function to register modules by
name, as well functions to determine whether a module or a list
of module names have been registered or get the list of currently
registered module names.  The main vtkweb modules now register
themselves using this api.

Change-Id: I195c39ae3c57f28c08ec87cb048134a7f18826a8
Added some code to allow web testing.  Also provided a stop function.

You can now pass an argument to the vtk.web.server that specifies a
Python script to run which can test the server.  The test script will
be run in a separate thread, and can send results back to the main
thread which will signal passage or failure of the test to the ctest
testing framework.

Adding a Python testing module to allow testing of vtk and pv web.

This module allows us to specify an extra command-line argument to
server.py which is a python test script.  The test script will be
run in a separate thread and can communicate it's results back to
the main thread.  All current and future ParaViewWeb applications
automatically have this testing capability.  Test scripts are now
specified as a separate python script in an argument to server.py.

This module also contains several convenience methods which can be
used by any test script.  Useful functions include methods for
indicating whether the test passed or failed, image comparison
methods, etc.

Change-Id: Ia0ada2c56540de9540524975d9865680e4cca5e2
Merge topic 'paraview-web-client-tests' into master

cd398d32 Added some code to allow web testing.  Also provided a stop function.
eadf5895 Added module registration api to vtkWeb, also added registration.