Phrase view

Many changes to support resource and operation reorg.

• Add an abstract PhraseModel class and a concrete ResourcePhraseModel class. A PhraseModel owns a DescriptivePhrase hierarchy and the SubphraseGenerator instances attached to it. The PhraseModel class maintains the hierarchy as operations and selections are performed by users. A PhraseModel may be configured by an SMTK views. PhraseModel provides some methods for its children to override that make managing the hierarchy much simpler.
• Add a JSON deserialization for smtk::view::View and test that it matches the equivalent XML description.
• Add an observe() method to resource manager. Now it is possible to get notified when a resource is added/removed. Note that the notification comes after the operation that reads the resource has completed.
• Track both resources and resource managers with pqProxy subclasses.
• Add a ParaView plugin panel that presents resources in a model-tree view.
• Provide minimal registration of the model manager to the resource manager.
• Add DescriptivePhrase::visitChildren() method for traversing a phrase hierarchy in order to update it.
• Fix issues with operator result creation. Model operators still need to use their Session's attribute collection to create the result while the new-style operators should use the operator manager. This will change again when the new operation manager is modified to use an attribute collection per operator rather than a single instance for the manager.
• Implement more of ComponentItemDefinition and partially implement XML I/O of attributes with ComponentItems (O only, no I).
• Provide some model-operator-specific code to copy result summary items from ModelEntityItems to ComponentItems with similar names (now also defined in Session.cxx). In the long term, ModelEntityItem should disappear.