Implement feature requested in issue #409 (default for connect)

Some accounts are used more often than others, so it makes sense to connect to that account with just '/connect'. You can set this account with '/account default set <account>' and remove it with '/account default off'.

The only qualms I have with this is that port, server won't autocomplete with '/connect port 9001 server this.isaserv.er'. An account needs to be specified for autocomplete.