rBStair v0.0.3

Simple tool for extruding stair. Update v0.0.3 -. No need to pick subobject polygon as firststep anymore. Now its done via sorting polys which atleast has 2 verts which are not shared with another poly -. Fix random missing riser. Thanks to ali shafiee for reporting the bug. Weld all vertices before extruding, also related to object pos from origin) -. fix nagging messagebox for original object deletion -. Set 2 materialID for tread and riser -. set subobjectlevel = 0 if subobject is still on when user create stair otherwise it causes weird viewport artifact