Integrated an object-oriented, phased approach to web testing.

With the integration of testing base classes written by Roni
Choudhury, we needed to refactor the existing web-based testing
scripts.  The introduction of these new base classes allows us
to support multiple baseline images and testing in different
browsers seamlessly.

Now, new test scripts should extend one of the three new testing
base classes: WebTest, BrowserBasedWebTest, or
ImageComparatorWebTest, and override some or all of the testing
phase methods implemented in those classes.  New tests can be
given any class name, and the class will be instantiated
dynamically at run-time by the newly refactored vtk.web.testing
module.

Also changed was the FindSeleniumDrivers cmake script, so that
at least the firefox webdriver extension can be found.  More
changes were required in the ParaViewTestingMacros cmake file,
where I fixed a bug that kept any but the first browsers tests
from being registered, and where I added a new argument to the
addition of test scritps: --test-use-browser.

Change-Id: Ie405280d2efefe13e0f09d7562ad15c7017a3628
Merge topic 'pvweb-integrate-test-packages-alternate' into next

5141f40 Integrated an object-oriented, phased approach to web testing.
Fixed test names, fixed broken element selection, viewport resize.

Test names now follow standard convention of prefix.testname.  Also
fixed a problem with the web visualizer can test where some element
name had changed in application and test could no longer find it.
Also now resize viewport explicitly in web tests so that different
broswers do not get different image sizes.

Change-Id: Icd1b27b5066875247e95054672116da9052e14af
Merge topic 'pvweb-integrate-test-packages-alternate' into next

b280128 Fixed test names, fixed broken element selection, viewport resize.
Update welcome and guide section

Change-Id: I1e37e80a78e0bf071313d8bd0ed97d6f2e490c05
Merge topic 'pvweb-doc-update' into next

0cd4843 Update welcome and guide section