[Scenario] Fix bug in expand/collapse

Fixes issues around expanding/collapsing timelines in a scenario (nasa/MCT-Plugins#145)

* Reflect proper pan/zoom characteristics in nested timeline-like components by:
  * Tracking visibility (so hidden, nested timeline-like components do not get "confused" into thinking they are top-level components which should control areas)
  * Firing change events to notify children when the top-level control has changed, so they know to accept the updated pan/zoom (necessary due to the layers of nesting in these components, e.g. graph in a timeline in a scenario). 
* Additionally, void flashing extra control areas (top and bottom bars with pan/zoom controls) by keeping more careful track of which components actually need to be added (that is, more carefully tracking when a timeline-like view is "actually" at the top-level, and should provide pan/zoom controls)