Add commander to the bot/server.

- Add dispatchCore into the bot/server to power the dispatcher and the
  commander.
- Add proxy methods from bot to commander for event reg.
- Fix some pointless locking.
- Make GetPrefix() in config return a rune. Backing still holds string
  due to the way yaml parsing works.
Add CoreCommands to the bot.

- Fix Commander to accept arguments correctly. Correct bad tests that
  provoked the bad handling.
- Add new AuthError to make better error handling for Authentication in
  Store.
- Add an initialized flag to the Store, IsFirst reflects this value.
- Expose data.UserAccessPwdCost for testing purposes.