Currently Marble's scale bar covers exactly half the width of the canvas.

Add a toggle menu entry to Marble's scale bar float item context menu that allows to reduce the width of the scale bar to a quarter of the canvas width. The menu entry should read "Minimize" and should be translatable. By toggling the menu entry the user can change the width of the scale bar forth and back between half and quarter the width of the canvas. The minimization state should also be implemented as a checkbox in the configuration dialog of the scalebar.