Audioreader - Advance pages (not just paragraphs)

**Context**

Often when I'm listening to a book, it is during transit on mobile. I listen to several pages at a time. When I return to the book (especially if its been some time) the page is not always correct and so I listen to snippets to re-find my place (which is typically off by several pages).

My only options for navigation are to move forward / backward one paragraph at a time (which requires 10 or so button presses to advance a page) or to stop audioreading, switch pages, and then restart audioreading (several times in a row) which is hard to do while in transit.

What I'd like to be able to do is just click the forward and backward button the scrubber to go forward/backward a page. But instead, the scrubber changes the current visible page without affecting playback.

One might argue that this lets someone listen to a book and jump forward to (e.g.) look at a figure on another page. But even this affordance is not especially useful because, as soon as the current active paragraph is read, the reader brings the patron back to the active page, loading the next paragraph (which effectively negates or diminishes potential advantages of previewing a different page than the one being read).

My proposal is that the back / next buttons on the scrubber should change the page and restart the audioreader from the beginning of the page or to add new buttons which go back / forward one page.

This becomes more complicated when we consider that on mobile, there **are no** back / forward buttons on the scrubber (in neither 1-up or 2-up mode) which I argue there **should be** for this reason.

In 1-up mode it's reasonable that scrolling pages shouldn't restart the audioreader. But in this case, I **should** have a way to advance the audioreader by a page (by clicking the next/previous buttons on the scrubber -- which are currently non-existent).

In 2-up mode, I do think that clicking on the next page should start the audioreader **iff the audioreader is currently reading**.

## Summary of Changes

1. On mobile, add left / right advance buttons back to scrubber
2. If left/right scrubber buttons pressed while in read-aloud mode (and reader is playing) then autoplay the new page
3. On 2-up mode, if a page is tapped/pressed to advance (and reader is playing) then autoplay the new page

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