adding ability to make animation

[shimwell]

It would be handy if the slicer can make an animation

Perhaps it could accept a tuple for some of these inputs of plane_origin, plane_normal, rotate_plot and then make an animation that sweeps between the inputs.

A nice tutorial on mpl animations can be found here https://brushingupscience.com/2016/06/21/matplotlib-animations-the-easy-way/