[FEM] fix typo
[FEM] fix typo

- the property has the name "Element order" thus the dialog should use the same name to avoid confusions

-also uniform naming for the element dimension and remove the redundant "Mesh" (is already in the UI groupBox heading

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