Feature request: remember last scroll position

Use case:
You're reading and scrolling a rather larger website and in the middle of it you want to go back to the top just to look up the article's date for example. But then you want to go back reading where you left off. Now you have to use a combination of d and j, which can take quite a bit of time and be bothersome. But if vimium would remember the last position before gg or G was hit, there could be a new shortcut for returning to the old scroll position.
Another scenario would be when you wanted to scroll to the bottom (G) to quickly take a glance at the conclusion of the article, but then you decide to continue reading.

I suggest gu or gb for this shortcut. (g-undo / g-back ). gb would be particularly good because
g and b are close on the keyboard, enabling one-handed usage.

The issue names no files, entry points, or tests. Start by locating the existing scroll commands and their handling of gg and G, then determine how a previous position can be retained and restored by a new shortcut. Done means returning to the position from before the last jump without disrupting normal scrolling.