Draft: clean up ViewProviderDimensionBase class
Draft: clean up ViewProviderDimensionBase class

Use methods to set up the properties. As the dimension object has
16 properties, these properties are assigned using three methods
corresponding to text, units, and graphics properties.

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