[Scenario] Build local controls only when needed

Only bother building local controls when they
are needed. Indirectly, this resolves
nasa/MCT-Plugins#145; additionally, it simplifies
run-time Swing component hierarchy.
[Scenario] Avoid flashing local controls

Avoid flashing timeline local controls in an
embedded view when toggling a collapsible
container.

* Track when component is actually visible
  (including ancestry) when determining if
  it is a top-level control which should
  include visible local controls.

* Fire a change event when a change to
  top-level controls has occurred; this
  is necessary to get contained controls to
  recognize the change in a timely fashion.
[Scenario] Clarify logic with comment

Clarify logic for rebuilding timeline local controls.
Merge pull request #147 from VWoeltjen/mctPlugins145

[Scenario] Fix bug in expand/collapse