Save sidebar state globally instead of per-document
For example, If I toggle off the sidebar, I want it to remain off next time I open another document, both to save myself the hassle of disabling it (it eats space I'd rather have for the document) and for performance (presumably thumbnails would not render when the sidebar is hidden). However, it applies to everything else too, like maximized state, size of the window, etc.
This is essentially the same as issue #82 (closed), but according to my testing, the sidebar still opens on startup because in @sudhanshuv1's !133 (merged) implementation (or somewhere else in the Papers code) the collapsed state gets saved per-document instead of globally (Evince used to save that globally, I believe).
This might be a regression from Evince, as there are a lot less codepaths now, and we might have chosen the wrong ones.