py4DSTEM.visualize.show() variables "min" and "max"

[cophus]

For all image plotting functionality in py4DSTEM.visualize.show(), I think we should consider replacing the intensity ranges:
min --> vmin
max --> vmax

min and max are standard python functions and so it seems best not to overload them as argument names too. Alternatively they could be replaced with a single variable:
intensity_range = [vmin, vmax]
since there are essentially no cases where one is set without the other.