[Qt] seed OpenSSL PNRG with Windows event data

- see https://bitcointalk.org/index.php?topic=113496.msg1228193#msg1228193
  for the initial suggestion for this
Yes but you do realize that randomness is one of the most critical parts of cryptographic software like this, and it's notoriously hard to test, so that change needs to be reviewed really carefully by multiple people.