Move the creation of animation to new script
`anim_eddy_contours.py`. `plot_eddy_contours.py` was becoming too
complex. Some of the options of `plot_eddy_contours.py` did not apply
to the animation. Plus we now want to iterate in
`plot_eddy_contours.py` on cyclones and anticyclones so we are going
to have to add complexity in `plot_eddy_contours.py`.