Allow seeing pool points contribution per-plot

[SlugFiller]

I want to see statistics to compare how much my plots contribute to my pool score. While the debug log contains messages about sending partial proof, it doesn't contain the plot key. The situation is even worse for an invalid proof, because I can't tell if it's an issue with a specific plot if I don't know which plot it's coming from.

I'd very much like to have that information. In the GUI, if possible. If not, then at least in the debug log, so I can gather and analyze it myself.