Add ability to show and hide "merged" Panels
Currently, one can show and hide each of the vertical panels (e.g., inspector, palletes, selection filter, play panel) independently either through the View menu or with a shortcut. Since they are often more than one panel merged, I suggest adding the ability to show and hide all the merged panels at once. See below for example of a "merged panel", on the right of the screenshot. Sometimes, when entering notes with two documents in view, I would like to hide quickly the merged panel to see more of the score.