Animation support

[henry2004y]

A while ago, the wrapper over Matplotlib makes it difficult to modify the plots afterwards, which especially causes problems when dealing with time series snapshots. The colorbar is so hard to fix. The solution is, instead of using level, provide a range of points.

The current support of animation in Matplotlib is not good enough, especially for interactive plotting and scanning through multiple snapshots. Based on what I've seen, Makie does a better job in this category, so I make a ref to #21.

More recent versions improve on the wrapper dramatically. Animations with fixed colorbars may become feasible, just as I do in Vlasiator.jl where you manually create a colorbar with fixed range. I will work on this if new simulation results require analyzing, and until then we will decide which way to go