Updates admin nicknames, moves list to txt file

http://tgstation13.org/phpBB/viewtopic.php?f=29&t=1164

Makes the pool of names used by a stealthmin's dsay use an external .txt list.

Updates the pool to the current admins.txt as of 9th August.

See thread linked if you're an admin and want to suggest a change to the list which I'll be sending to SoS when this gets merged.
Shouldn't you put the removed nicknames in here?