* `MapOnSketch` is active only when there is a sketch available
in the document.
* `ReorientSketch` and `ValidateSketch` are active only when one,
and only one, sketch is selected.
* `MergeSketch` is active only when there is at least two sketches
selected.
* `MirrorSketch` is active only when there is at least one sketch selected.
Clean up the lines so they are not extremely long.