Consider using scrolled mode as default for EPUB files in the Reader

[mrtcode]

I know that on the client we default to paginated mode because of the performance reasons for some EPUB files. As there is no way to switch between modes, I suggest to use scrolled mode in web-library reader because it's more convenient, and the performance issues likely be less prominent in regular browsers.

We should be able to enable the mode with this:

createReader({
...
state: {
  "flowMode": "scrolled"
}
...
})

https://forums.zotero.org/discussion/110550/android-13-smartphone-with-epubs-scroll-versus-page-down-image-sizes

@AbeJellinek