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.