Add test for removing the celltoolbar
Add test for removing the celltoolbar

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