Move stats into a separate class.

This "breaks" (read: does nasty things to) the TriviaTaunter. The
taunter relies on being able to get the stats from the bot... which no
longer has the stats... well it does. It's a stupid hack now :).
add rudimentary stat persistence
decouple the leaderboard from the bot

... by allowing plugins to find other plugins by class name (this is
probably a shit interface. OH WELL. STOP READING MY LOGS)
Move plugin configuration to bot.yaml

All the plugin classes and configurations for the plugins are now stored
in bot.yaml (hardcoded config file name - fix this)