Add a toolbar button which allows to show and hide single lines.
A neat feature would be a toolbar button which allows to trigger the visibility of all and single lines. This would depend on #4.
There should be a simple toolbar button...reminds me that we need an icon...which holds a list of all lines (Direction, location and location type should be enough, like
Horizontal 80px and
Vertical 20char). Upon click of one of the items, the visibility of that line is triggered. An additional option to hide all would be nice.