+ Implement `PhraseModel::handleCreated()`.
+ Hold expunged model entities rather than UUIDs.
Change `smtk::model::Resource::deleteEntities()` so that the expunged
container holds `Entity` shared-pointers rather than UUIDs;
this keeps the entity records from going out of scope as they are
removed from the model resource (long enough that the operation result
can be processed to remove them from the UI).
+ Properly remove phrases of deleted components.
This also removes overrides that ResourcePhraseModel provided for
handling operation results; the base class implementation should
do what is needed without further work by the subclass.
+ Provide a flatter (two-level) resource tree.
+ Documentation for views and phrases.
+ Improve sorting of descriptive phrases
by comparing smtk::resource::Component subclasses and
model entity types.
+ Show a valid icon for lists, not the invalid icon.
+ Eliminate some warnings from other parts of SMTK.
+ Make subphrase generator a user preference in the ParaView extensions.