Collapsible Panels

Tools like the Mixer and Timeline are really useful, but they take up a lot of real estate, especially when working just on my laptop screen. I'm aware you can open the individual tabs with F10, F12, etc, but that means you have to close everything in the panel to get the screen back, and reopen one-by-one.

It'd be great to be able to collapse the panels whilst maintaining the open tabs, double clicking (or something) to toggle between open and minimised. I've mocked up a visual example of what I mean.