Problem: minimize application, restore it and the module panel disappear
When the application is minimized, QDockWidget receive the HideEvent and
fire its signal visibilityChanged that got connected to the menu QAction
which fire its own signal toggled(bool).
If the QDockWidget::setVisible(bool) is connected to this toggled() signal
setVisible(false) would be called and really hide the QDockWidget (before
it wasn't really hidden, see QWidget::IsVisibleTo() for more info).
To avoid all this issue, QDockWidgets::setVisible should only respond to
the triggered(bool) signals of the menu QAction.
For consistency, apply the same logic to the QToolBars and their associated
menu QActions.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@15645 3bd1e089-480b-0410-8dfb-8563597acbee