Organize mixins

[thirdcreed]

• [x] Organize extensions, and voting ;methods into a logical folder structure
• [x] Consistently name all iteration over candidates: "ballots"
• [x] Consistently name all "dominanceMatrices": "pairwiseMatrices"
• [x] Find a place for blank score sheets, and repeeated logic in voted methods.

[thirdcreed]

Right now things are a bit inconsistent, because I've been implementing different methods individually to see which elements repeat.