Polishing fitting functionality

[mkhorton]

• Why does minimum score 0 not work?
• Be able to supply scores by default in Graph construction
• Think about how to report error in aggregated quantities

[clegaspi]

Regarding the minimum score of 0, that was a constraint Joey added, that the minimum must be 5% weight. @montoyjh was there a specific reason?

[mkhorton]

Yes, I understand the default is 0.05, but if you set it to 0 the fitting just doesn't work.