New module for moment stuff. Called Coltrane. Very cool.

This builds off a lot of the tests in moment_tests
plot_line() now only generates the figures if it's going to show them.

This frees up a lot of memory on large runs
Force the size of a galaxy simulation to be a square of an odd number.

So the center is easier to define.
Added function to generate fits version of goodness-of-fit map