Some notes about how to properly manage toolbars in views : saving and
restoring them, and making sure the "show xxx toolbar" menu items are
in consistent state.

+ We use KMainWindow::setAutoSaveSettings() to do most of the dirty
  work.  It is always called at the end of the view ctor. This is
  important because all toolbars must be created prior to calling
  setAutoSaveSettings.

This handles both the saving *AND* the reading of bars settings
(visibility and position).

+ What remains to do is setting the various "Show XXX Toolbar" toggle
  actions in a state consistent with what was read from the
  options. This is done by checking if the corresponding toolbar is
  not hidden (checking if it's visible won't work, because when this
  occurs the toolbars are not yet shown). E.g :

m_viewTracksToolBar->setChecked(!toolBar("tracksToolBar")->isHidden());

+ So there is *NO NEED* to save these toggle actions state. We just
  deduce their state from the related toolbar's state.

+ The case of the editview (notation, matrix) is a bit special. These
  are derived from EditViewBase, which has readOptions() and
  slotSaveOptions() methods, which should be called by their children
  (even though they currently don't do much).

EditViewBase::readOptions() handles the "show toolbar" and "show
status bar" actions. It should be called right after
setAutoSaveSettings() by the child. That is, children of EditViewBase
should explicitely call EditViewBase::readOptions() in their own
implementation of readOptions().

On the contrary, EditViewBase::slotSaveOptions() is called by the
EditViewBase dtor. There is no need to call it explicitly in the
children's dtors.

+ When adding a new toolbar : if this toolbar has a corresponding
  "Show" toggle action, then the only thing you need is to make sure
  this action is in the proper state according to the saved status of
  the toolbar. Just set its state as indicated above.

