Plaintext password should not be stored

When AuthSystem.System is set to Authme, if a player is logged in through website and his info is not stored in WA_Players, the plugin will insert a new row and use his plain text login password as password column, which is not necessary and causes secure problem.

Here is a quick fix, insert null string instead of plain text password.

workaround for http://dev.bukkit.org/bukkit-plugins/webportal/tickets/68-web-portal-stores-plaintext-passwords-in-db-when-auth/