Narrative Viewer = introduce Only show visible entries toggle

[IanMayo]

The Narrative Viewer only displays visible narrative entries.

But, there are occasions when analysts wish to use the Narrative Viewer to control which narratives are visible.

Analysts hope to exploit narrative data better in the future - so managing which ones are visible will become more important.

So, we could do with:

• a Only show visible entries toggle in the View Toolbar and View Context menu
• a Visible column in the data, to allow view/control of the isVisible() property. Ideally we'd also have Select All and Select None buttons _somewhere. So, the analyst could follow this flow:
  • show all entries
  • select all
  • set visible to `False
  • show CO Comment entries
  • select all
  • set visible to True

This would cause just the CO Comment entries to be visible. The value of Only show visible entries would be persisted within Debrief.