Minimizing panels isn't (correctly) reversible

[Alv]

If the user minimizes one of the right hand panels by mistake, they can't revert that action easily and in full: unminimizing the same panel leaves all panels with a modified size, and they have to be resized manually.

It's quite easy to click on the panel title bar when one wanted to click the line just below it. Workaround could be that only clicking the leftmost downward triangle button would minimize the panels, not the whole title bar.

Ui actions should be reversible.