Add update_or_create_student api method
Add update_or_create_student api method

ellisonbg/nbgrader,jupyter/nbgrader,dementrock/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,alope107/nbgrader,EdwardJKim/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jdfreder/nbgrader,ellisonbg/nbgrader,MatKallada/nbgrader,jupyter/nbgrader,modulexcite/nbgrader,modulexcite/nbgrader,ellisonbg/nbgrader,EdwardJKim/nbgrader,EdwardJKim/nbgrader,dementrock/nbgrader,ellisonbg/nbgrader,jhamrick/nbgrader,EdwardJKim/nbgrader,alope107/nbgrader,MatKallada/nbgrader,jhamrick/nbgrader,jdfreder/nbgrader