Respect pre-paginated page spreads

[mikkelvp]

No description provided.

[fchasen]

Sorry for the delay reviewing this. Is there an epub I can test it with?

[mikkelvp]

Sent you an email.

[fchasen]

Sorry again for the delay on this, thanks for making these fixes - they look great.

[johnfactotum]

This PR works great! But there's a slight issue when going directly to a spine item with the property page-spread-right with rendition.display().

The issue can be reproduced like so:

1. Open the book "Page Blanche" from EPUB 3 Samples with Epub.js 0.3.87
2. Run rendition.display(6)
   Actual result: section 6 is displayed on the right side, but the left side is empty
   Expected result: section 6 on the right and section 5 on the left
3. Now run rendition.prev()
   Actual result: section 5 shows up on the right, and section 4 on the left
   Expected result: section 4 on the right, and section 3 on the left

[mikkelvp]

@johnfactotum I'm aware of this. I will look into it sometime in the future.