Initialize mark and add compatibility for rebar.RebarShape
Initialize mark and add compatibility for rebar.RebarShape

- Initialize rebar mark with rebar label
- Add compatibility for attribute rebar.RebarShape to work with changes
  done in this PR:
  https://github.com/amrit3701/FreeCAD-Reinforcement/pull/65/commits

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