Add per-view, per-component visibility edits.

• Visibility editing in the SMTK resource tree, in all its glory. Consistent, per-view component visibility editing, including:
  1. Toggling of pqPipelineSource visibility when a resource's visibility is edited.
  2. Immediate updates of all eyeball icons in the entire tree when one component's visibility is presented multiple times.
  3. Immediate updates of all eyeball icons when the active view changes.
  4. No eyeballs displayed when the active view is null.
  5. Proper decoration of resource phrases so their visibility may be edited.
  6. Sorting of phrases by default.
• Other GUI components (besides the SMTK resource tree) may call pqSMTKModelRepresentation::setComponentVisibility() and the resource panel should stay up to date. This is in anticipation of RGG, which wants to change pin/duct/assembly/core visibility in response to what's being edited.
• Adjust the color and opacity used to render selected entities. By default, the selection should be rendered as a translucent overlay. This removes problems with z-fighting and allows users to see when visibility has changed on selected entities.
• Do not add color arrays to model-entity polydata (in the vtkModelMultiBlockSource). This wastes space; instead, entity color is now stored as field-data in an array named "entity color". However, this field data is currently ignored by the model representation in SMTK's ParaView plugins; instead, the model resource itself is asked for color property information. The "entity color" array is stored so that ParaView and VTK filters ignorant of SMTK can make use of it.
• Change "mixed-dimension cell(s)" to "cell(s)" in model-entity summaries. This is less confusing to users. And more concise.
• Fix a crash when the resource loader fails. This can happen when the plugin for the type of session contained in a resource's file is absent.