Follow through on changes required by resource inheritance.

There are consequences to making everything (mostly) in SMTK inherit either Resource or Component. A bunch of stuff related to model entities needs to be generalized to deal with resource components of any type. This commit moves classes around and/or provides alternate versions to accomplish this.

• Add a new top-level SMTK subsystem named view for dealing with presentation of resources and components to the user.
  • Note that smtk::common::View should move here at some point.
  • Make a new DescriptivePhrase and SubphraseGenerator in smtk::view. These are extremely similar to the versions in smtk::model but deal with components of any type. Eventually, the versions in smtk::model should disappear.
  • Add new phrase types to the view subsystem:
    • PhraseList which replaces EntityListPhrase and more
    • ComponentPhrase which replaces EntityPhrase
    • ResourcePhrase which displays the filename holding components.
  • Add the unitDescriptivePhrase test in smtk/view/testing/cxx that will print out a hierarchy that contains most of the information that was in the previous model-specific tree.
• Add a new ComponentItem and ComponentItemDefinition to the attribute system. This will eventually replace both ModelEntityItem and MeshItem and will allow attributes to be associated to mesh sets as well as model entities.