fixed shutdown bug.

[shawshark]

save players accounts on shutdown.

[niccholaspage]

This should already happen, look at this method: https://github.com/niccholaspage/Fe/blob/master/src/org/melonbrew/fe/database/Database.java#L148

[Relicum]

What will failure due to the way HashSet and sets in general work. You need to use a Iterator. In my fork I fixed here is the code to fix the method.

    public void close()
     {
        Iterator<Account> iterator= cachedAccounts.iterator();

       while(iterator.hasNext())
        {
            Account account = iterator.next();
            account.save(account.getMoney());
            iterator.remove();

        }