Fix help display when using webengine

• Fix integration of Qt WebEngine module in Paraview. The cmake option was never passed down to the C++ code so when PARAVIEW_USE_WEBENGINE was activated, a QTextBrowser was used to display help instead of a QWebEngineView.

• Add JavaScript files as valid ressource for documentation.

Below is a GIF of the carousel added as an example in Examples/Plugins/ElevationFilter.