Make the geometry of the minibar user-configurable

As well as the width of the toc notches
Lower the default value of the container size a bit to avoid eating into
the last line on small borders setup (I checked on 167 & 212 DPI
devices, Feel free to revert to the previous value (19) if that causes
trouble).
Merge pull request #783 from NiLuJe/master

Make the geometry of the minibar user-configurable