late night optimizations

-isMemberOfSets returns true/false instead of 1/0
-when loading the posts of a topic only get the userdata for each user
once, before this commit if a topic had 10 posts from 2 different users
we were getting the user data for each user 5 times (drunk)
-getVoteStatusByPostIDs and getFavouritesByPostIDs no longer make
pids.length calls to the db, they use isMemberOfSets now
-getUserInfoForPost renamed to getUserInfoForPosts and doesnt make
uids.length calls to db, uses getMultipleUserFields instead