Move HelpBrowser to QWebView

[DaneGardner]

The HelpBrowser object (in the Help plugin) is subclassing QTextBrowser, which has some support for cascading stylesheets, but doesn't fully support them. This sets up a horrible looking set of documentation (i.e. the Doxygen docs) for the in-GUI help system. We need to move the object over to subclassing the QWebView object, which supposedly fully supports stylesheets.

This is probably a Phase II issue