Review whether the legacy Help panel (pqHelpReaction::showHelp) should be shown.
As of CMB 4.1, the legacy dialog was hidden, instead, ModelBuilder exposes CMB and SMTK pdf user guides (generated from the readthedocs).
It is necessary to review whether this panel could be useful to show additional documentation, otherwise some things could be removed from
pqCMBModelBuilderMainWindow. Likewise, if other applications in CMB would be taking the pdf approach, then their concrete MainWindow classes (and the base class) would need a cleanup.