toolbar improvements

[absurd-turtle]

following improvements for the toolbar shall be implemented:

• [ ] Disallow marking the text "Layers"
• [ ] don't show scrollbar if not needed
• [ ] remember sizes and arrangement of toolbars (per user)
• [x] #570
• [ ] Some browsers (e.g. vivaldi) always show big white scrollbar
• [ ] side bars should take whole site (from top to bottom)
• [ ] Main layout: the bars left and right should be from very top to very bottom, so the language bar etc. should be in between
• [ ] Bar cannot be reduced to zero
• [ ] Minimum size introduces a horizontal scroll bar
• [ ] resizing problems: when you see all the layers and then you resize layers to nothing: when scrolling slowly it works, when scrolling fast there is different behavior ("Layers" scrolls up)