unnecessary scroll bar displayed in reflow view (pan-zoom viewport overflow:auto?)

[Kathybluefire]

If you watch this flow, you'll see a couple areas of concern. Maybe by design, and if so, then there is no issue, but wanted to bring up to be sure.

1. Open Reflowable Doc with the browser full screen and you see the default -- spreads
   
2. Drag the browser horizontally until the aspect ration is taller than wide, and the content goes to single pages. Expected.
   
3. Open the Table of Contents and you get a superfluous scroll bar on the right. Why?
   
4. Set the User Setting to Spreads and we lose the aspect ratio rule and can have long thin pages by scaling the browser horizontally. One would think the single page in proportion to the content window would hold up, even if the user selects spreads. Is there a technical reason why it doesn't?

[danielweck]

User preferences take precedence, even if the forced two-page spread results in narrow columns of text. So that's okay.

However the scroll bar is problematic, and was reported before (although I could not reproduce this myself). I think the culprit is the pan-zoom feature for fixed layout documents, which allows overflow:auto on the viewport (for panning). This needs to be fixed.

[danielweck]

Scroll bar fixed here:
readium/readium-shared-js@6b89df6