[Sketch] improve wording for a color
[Sketch] improve wording for a color

as discussed here: the wording "datum color" does not make clear what it is about. It is in fact the color for dimensional constraints, thus name it as such

- also fix the dialog height (found and automatically corrected by Qt Designer)

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