Do not put plots under version control

[rmcdermo]

@leventon Why are these png files under version control?

People are starting to actually use this repo now. We need to get this stuff in order. If you need to add Jupyter notebooks to show plots from data, then do so. But do not commit png files.

[rmcdermo]

I added a new tag v0.0.0-figures. If you want, you can create a release with this tag and put any figures you need here, then link to them. I also created a similar tag for macfp-db-figures. We should begin migrating all the images for macfp-db over to that release. (Should have done this right at the beginning, but now this is becoming a problem, so we should clean it up.)

I am not suggesting you overhaul all figures right now. This issue pertains directly to plots made from data. These plot should not be under version control. If you want to identify the plot with a commit, then add a tag to the plot that indicates the commit of the data used for the plot.