WIP: Move representation classes / Additional representations

• Move DescriptivePhrase subclasses (that describe content) into a PhraseContent class, instances of which are owned by DescriptivePhrase. The plan is to separate the hierarchy of subjects from the content of the subject so that attributes of the subject can be overridden via the decorator pattern. This leaves phrase lists with improper descriptions since the common/union flag values are not set properly (among other things).

• Start trying to display "eyeball" visibility icon selectively -- only when the PhraseContent advertises it as available.

• Use a the new visitor method of vtkCompositeDataDisplayAttributes to fetch per-view block visibility information from mappers.

• Try to keep ENTITYID out of SMTK except for the vtkModelMultiBlockSource.

• Attach UUID to both the multiblock metadata and the actual vtkDataObject instance. The latter is preferrable in almost every instance since it is then possible for methods passed only a data object to get its UUID. This is necessary for the PV representation's visibility modification queries to work properly since, when iterating over visibility entries in vtkCompositeDataDisplayAttribute, only the block is available, not its metadata.

• Move representation classes to the smtkPVServerExt and smtkPQComponentsExt libraries. This is necessary to avoid cyclic dependencies between the representation and the resource panel (which will soon display/modify the representation's visibility information).

• Expose subtypes (wireframe, surface with edges, etc.) and additional representations (outline).