Stats managers

[emilydolson]

This adds in an object that can track open-ended evolution stats, as well as update signal. Technically the OEE stats manager is in working order, but before we merge it in I/we should probably:

• Refactor some of the code in OEE.h into LineageTracker.h
• Come up with a better way to set parameters
• Figure out roughly what the plan for stats managers going forward is
• Create a base stats manager class for this to inherit from (I gave up because I couldn't come up with common functionality all stats managers should have)
• Make it interface nicely with the world object, like the other managers do (ideally it should get the fitness function from the org_manager).

(sorry I didn't make this sooner - I forgot about #27)