Use openssl random for CSRNG, remove more unused code

- Use openssl_random_pseudo_bytes as a CSRNG for password and salt
- Removed these three options from _parse_sql because they are not
actually used anywhere:  crypted password, dovecotpw, hashed passwords
- Password is now stored in whatever format the configured SQL query
decides to use. This means passwords would have to be stored in
cleartext if you are using Sqlite since it doesn't have a hash function.