+ Move smtk::resource::SelectionManager to smtk::view::Selection.
  It really isn't a manager; it's a selection. Each instance holds a
  map enumerating the "degree" to which each component is selected.
  You can have multiple selections in an application.

+ Make the ParaView SMTK resource panel respond to selections
  and emit its own. Note that selecting a summary phrase does not
  result in entities in its child phrases being selected. This
  is a departure from the previous phrase view; we may add
  this functionality into the new resource panel at some point
  as it satisfies the priniciple of minimum astonishment.
  The problem is that it requires computation of child phrases,
  which destroys the lazy nature of the algorithm.

+ Fix resource handling when deleting sources.

+ Add a VTK-based attribute "reader" (that produces a pretty empty multiblock
  but has the side effect of adding a resource to the resource manager when
  an observer is attached).

+ Port more code over from old, model-only EntityListPhrase to PhraseList:
  generate more descriptive titles for lists with many, potentially disparate children.
  For now, this only deals with model, not mesh or attribute, components.

+ Adds a currently-uncompiled "unit test" for a component item UI.

+ When inheriting QStyledItemDelegate, do not call the inherited
  `paint()` method inside your own as it will draw each item's
  `Qt::DisplayRole` text overlapping your own.