factions: improved isPlayerInFactionType return

Fifth return argument gives information about the player leader status.
Also added an additional chatbox output to warn if group doesn't exist.
chat: added /clearchat command

Clears up the chatbox, pretty much.
players: added an array key for canBeFactioned

Used by groups.
police: fixed a few issues and added a command

/arrest for arresting; also splitted jail information into its own file.