Sketcher: clean up general commands tooltips
Sketcher: clean up general commands tooltips

* `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.

Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master