Implement lexicase scorer

[NicMcPhee]

A simple use of lexicase would be to have every potential solution have two values:

• The total value (big is better; ignores capacity)
• The total overage (small is better; 0 if we're at or below capacity)

We can then see if lexicase can do something useful with those two values. My guess is that it will put too much "energy" into exploring "solutions" that are essentially "including everything", but I don't know for sure.