Align sidebar's separator with editing area visually
Align sidebar's separator with editing area visually

Tweak placement of the horizontal separator between upper and lower
sidebar areas to match the editing area's borders perfectly. Fix HiDPI
width. Use lighter color, from editing area, to match it.

c72578/poedit,alexhenrie/poedit,nawawi/poedit,vslavik/poedit,nawawi/poedit,c72578/poedit,PKRoma/poedit,nawawi/poedit,vslavik/poedit,alexhenrie/poedit,c72578/poedit,vslavik/poedit,alexhenrie/poedit,vslavik/poedit,alexhenrie/poedit,PKRoma/poedit,alexhenrie/poedit,PKRoma/poedit,vslavik/poedit,nawawi/poedit,c72578/poedit,nawawi/poedit,c72578/poedit,PKRoma/poedit,PKRoma/poedit