StoryCacher: keep converting 3 newlines to 2
fix story test after 285fd82c
bring back story downvoting, remove low quality option

story hiding is still here, so hopefully this will result in less
bogus story downvotes
enforce a maximum username length of 25
fix story caching stuff once and for all
shrink story hotness window to 24 hours
don't include hiders in story vote summary
don't mail stories and comments to users that have hidden that story

closes #141