This function returns some information about the given party-id's leader. When type is ommitted,
the default information retrieved is Character name of the party leader. Possible types are:

1: Leader account id
2: Leader character id
3: Leader's class
4: Leader's current map name
5: Leader's current level as stored on the party structure (may not be
current level if leader leveled up recently).

If retrieval fails (leader not found or party does not exists), "null" is returned instead of character name,
and -1 is returned for the other types.