Add support to backup and restore single windows

[HikariWS]

I recently started using TabFern. I've been using Tabs Outliner for a few years, currently I have almost a thousand tabs on it and am trying to replace it because it's closed sourced and its owner is gone.

I tried TabFern's backup and restore, I loved how it allows choosing where to save and read its backup file, that makes easier to keep them on cloud storage.

But it's troubling to save all windows at once, and then duplicate them all when restoring. It'd be much easier to add backup and restore commands on windows context menu. This way we could backup a single window, which includes having files sets separated for each window. And also be able to restore a window from a file, keeping it on its ordered place, and just replace its tabs.

[cxw42]

Related: a comment from Xalomon 2022-04-25 on the Web Store reviews page:

When trying to restore a backup of a lot of tabs they all will be loaded in memory and make Chrome crash, unlike recently closed that loads them suspended and doesn't have this problem.