UI Tweak: Collapsible driver variables in Drivers Editor

It's a simple thing, but it would certainly help a lot.

In the Drivers Editor when you add variables you get all those little panels similar to the ones for hooks or modifiers, which are able to collapse and reduce visual clutter while editing input fields.

It would be great if the variables panels in the Drivers Editor could do that too. I sometimes use quite a few variables in my drivers, which I use heavily, and it can be a pain scrolling down every time I need to tweak a value.

Another small and useful addition would be the ability to copy individual driver variables as well as all of them at once.