Change username with /cmi nameplate command

[vano04]

Description of feature/improvement request:
allows you to use the /nameplate command or a new command to allow you to change your displayed player name to anything. A /disguise plugin would work just as well but I seem to think that implementing it with /cmi nameplate will work better for all.

Detailed explanation of what it should do, when and in what situation:

It should change the username above a player's head not just the prefix and suffix.

Basic explanation as to why this feature is needed and/or useful to have:

To allow staff to disguise as a player when investigating an issue or just for fun.