Add recruit role for factions

The recruit role's goal is to enable factions to invite new members without being afraid of getting griefed instantly.

Adds a configuration option "factionRankDefault" for default rank of newly joined faction members. By default this is RECRUIT, but it can be set to any supported rank.

Adds the /f promote and /f demote commands, which leaders and officers can use to increase or decrease the rank of a faction member by one level, up to officer, or down to recruit.
This version of the recruit feature preserves the /f officer command for backward compatibility.