add player variable to the clearchat command

[CloudeLecaw]

currently we can clear the chat for all or our self.
well admins should have also have the ability to clear the chat for other player or trigger events (or from console) that clear the chat for a target player.
So it would be nice to have the playerName variable as an extra optional variable
cmi clearchat ([playerName]) (self) -s
to avoid missuseage this should be have ab extra permission like it does for other commands
cmi.command.clearchat.others