Streamlining

[pmelchior]

This PR streamlines common tasks.

• Blend.fit writes logger message with number of iterations and final logL
• display.show_likelihood shows our convergence plots from a fit Blend instance.
• display.show_observation shows the image and PSF in common norm and size (like show_scene but without sources)

In the process, I renamed loss to log_likelihood in both Blend and Observation, and fixed the stupid -1 for good.

[fred3m]

This looks good. The only change that I requested is to make logger output an info instead of a warning to show the final logL, since this isn't really indicative of something that went wrong and will pollute peoples consoles/terminals.

[fred3m]

This seems more like info than a warning.

[fred3m]

Of course, the docs are failing to build, as well as some changes that are needed in scarlet_extensions since you changed the name of Blend.loss. So either deprecate Blend.loss or fix scarlet_extensions using a branch with the same name.

[pmelchior]

I will re-introduce Blend.loss to be backward compatible.

As for logger.warning, I am aware that it's not formally a warning, but it's the default visible value, and I think it information most people would like to see after Blend.fit.