+ Switch the plane-item widget to use the new display-sized plane widget.
+ Add a coordinate-frame item-widget.
+ Add an "operation" for inspecting meshes.
  The operation does nothing; its parameters will have custom
  widgets that add mesh inspection to the operation panel.

Supporting changes include

+ Allow an attribute's association item-widget to be customized.
  Also, make qtAttributeItemInfo accept shared pointers by const reference
  rather than by reference so the main change will compile (which requires
  dynamic shared-pointer downcasting).
+ Add a reference-tree qtItem widget. Combined with the change
  above, this widget provides an alternative to qtReferenceItem
  for attribute association; it takes more screen space but
  provides better visual feedback.
+ Move widgets out of plugin directory.
  The smtkPQOperationViewsPlugin needs to call methods specific
  to pqSMTKPlaneItemWidget which it could not because the class
  was inside a plugin (not a library) and its symbols were not
  exported.
  Move all the widgets into the smtkPQWidgetsExt library and
  export their symbols.
+ Remove unused method `qtBaseAttributeView::requestModelEntityAssociation()`.
+ Extend membership badge to be pickier about applicability.
  The badge configuration may specify a rule and a filter for
  determining which descriptive phrases will display the badge:

  + The default rule accepts all phrases while others require
    the subject of the phrase to be an object, component, or
    resource. Additionally, the subject may be required to have
    renderable geometry.
  + A filter, if present, is applied to all components (and only
    components – not resources or other persistent objects)
    that would otherwise be displayed.

  The purpose of these configuration options is to accommodate
  operations that wish to pass geometry for several components
  to be processed.
+ Have the resource multiblock source pass all geometry, even
  volume meshes, straight to the output. This will allow ParaView
  filters downstream access to volume data.
+ Provide methods to print view configuration data for debugging.
+ Add a method for property widgets to request a render.
  This is used by the pqSMTKSliceItemWidget to cause a
  render when the slice inputs change.