Add Landmarks to Navigation

[nicpottier]

From @elasticsounds

TOC vs. Landmarks
In this version the TOC is generated and works great, however we are not getting landmarks like Cover, Credits, TOC, Start of Book, End. These landmarks are useful for material like storybooks which don't have a natural TOC and make sense for other similar content types.

We may want to consider a "landmarks.json" with these. It can be added to the nav bar on the left with the TOC and could be useful as a fall back if no actual TOC exists. We might just also want to add landmarks to the toc.json, but ePub guidelines list landmarks as a different concept.

[elasticsounds]

[elasticsounds]

An example of a storybook with blank Table of Contents. Consider creating landmarks for Cover / Start of Book / End?

[nicpottier]

Instead of generating new things how about just hiding contents when there is nothing in it?

[nicpottier]

(to be clear I'm talking about the contents tab, not contents entirely)

[elasticsounds]

From a perspective of blind user, what landmarks would be useful for navigation? Maybe cover, start, end???