Move save_figure_widget to matplotlib only
Move save_figure_widget to matplotlib only

This doesn't apply for 3D, so just move it into the matplotlib
viewers.

yuxiang-zhou/menpo,grigorisg9gr/menpo,menpo/menpo,patricksnape/menpo,patricksnape/menpo,patricksnape/menpo,mozata/menpo,mozata/menpo,mozata/menpo,menpo/menpo,menpo/menpo,grigorisg9gr/menpo,yuxiang-zhou/menpo,yuxiang-zhou/menpo,mozata/menpo,grigorisg9gr/menpo