[2c] Render the continuous view from segment pages #437

Part of Phase 2 (#425) of the data layer plan.

Continuous view over segment pages, through a segment range of its own rather than the segment list's useSegmentWindow range, which culls by the list's vertical scroll.

Done when: the strip renders from segment pages and flattens only its own segment range; in the app on WEB it matches main on opening a book, after scrolling the strip to both ends of the book, after a jump to an unloaded chapter, and after a boundary edit and a phrase link made in the strip.

Depends on: 2b (#436).