update: First implementation of Karma module.

*  Added karma.py with implementation of Karma that gives/removes virtual karma points to/from users.
*  <user>++ increases karma of user by 1 for every 2 pluses.
*  <user>-- decreases karma of user by 1 for every 2 minuses.
*  !karma 'user' shows karma for 'user'.

Signed-off-by: Jakub Novak <jakub.novak@gmail.com>
Do you really need BotPlugin, event and threaded here?