+ Allow a subclassed qtDescriptivePhraseModel instance to be passed to
  its constructor.
+ Make the ParaView-specific visibility decorator available for other
  ParaView plugins to use.
+ Expose the qtResourceBrowser's QTreeView.
+ Move most of pqSMTKResourcePanel into qtResourceBrowser (Qt parts) and
  pqSMTKResourceBrowser (ParaView parts).
  This will allow easier customization, and particularly
  allows people to use the widget without it being central to
  a dock widget, making it simpler to configure components in
  the widget that are needed at construction time.
+ Also, make pqSMTKResourcePanel::Internal::m_phraseModel point to
  the base class (PhraseModel) rather than the particular subclass
  we use (ResourcePhraseModel).
+ Better nullptr testing to prevent crashes when invalid QModelIndex values
  are used.
+ Test whether the model passed to qtDescriptivePhraseDelegate::editorEvent
  is a QAbstractItemModel such as QSortFilterProxyModel; if it is, then map
  the index.
+ Store descriptive phrase pointers in QVariants and provide a way to
  obtain phrase pointers from a QModelIndex without access to the
  underlying QAbstractItemModel.
  This allows clean separation between our QAbstractItemModel subclass
  and classes that consume its QModelIndex instances.
  The separation makes it possible to pass a QAbstractProxyModel to
  use instead of a qtDescriptivePhraseModel so that searching can
  be exposed in the GUI.