Preserve scroll position

[Infocatcher]

Initial state:

[ Some starred/bookmarked entries ]
[ Some skipped entries aka "to read later" ]
[ Entry with "mark entry as read" button under cursor ] (we read from here and down)
[ Some unread entries ]

Now we can just click on each next entry to mark it as read and hide (and don't move mouse!). But not for some last entries.

I'm use following style as a workaround: https://github.com/Infocatcher/UserStyles/blob/8ae664932d903b3815ab94ee0dc3dbce0be3f816/Brief_Compact/brief-custom-style.css#L24

So I have some empty space after last entry. And last entry may be on top of the page.

But I had to change https://github.com/Tanriol/digest/blob/master/chrome/content/feedview.js

// Minimal number of window heights worth of entries loaded ahead of the
// current scrolling position at any given time.
const MIN_LOADED_WINDOW_HEIGHTS = 1;

from 1 to 1.5. And it's would be good to add option for this.

[tanriol]

I'd prefer a patch making enoughEntriesPreloaded use not the total window height, but the bottom of the last entry position. It would be a cleaner solution.