Organize Classes

[carlschroedl]

Currently the src and test classes are both in one flat folder due to ignorance about how PHP namespaces and autoloading work.

Some ideas for organizing:

• We could move all of the basic classes like Candidate, Margin, Ballot, NBallot, Agenda, (did I miss any?) to a "domain" or "model" folder
• GenericCollection and its subclasses could go in a "lists" folder
• Calculator classes could go together
• Comparators could go together
• TieBreakers together

Not sure where Grouper or RankedPairGraph would live