More work on karma/voting system
- fix bug in start.php so $user.karma file is written with default value
- add plus/minus button css
- add buttons to theme
- add buttons to thread.php sp urls are created correctly

still to do:
- remove buttons when
  + user is not logged in with http auth (don't want to have to enter username/pass just to +/-)
  + user has already +/- a post
  + user does not have a high enough karma
- probably rename 'karma' to 'reputation', if i can be bothered
- handle plus and minus requests on a post/reply