Maximize and drag+drop for panes

[hopperelec]

To the right of the minimize button should be a maximize button (🗖). When clicked, the tab should become the only one shown. When clicked again (🗗), previously shown tabs should reappear.

[hopperelec]

I've discovered a React library which does exactly what I had in mind for the panes, and I've found a a Svelte library which attempts to be a port of that. While it doesn't seem as fully-fletched as the original React version, I think I will switch to using it and then try and make a PR to that for any features from the original that I can port over. That way, other projects can benefit!