Add Atlantis.app v0.9.9.4

Atlantis is an OS X MUD/MUSH client. It hasn't been updated in a while but is
still one of the better MU* clients on the platform.

Plain app bundle, no install/uninstall process needed.
Merge pull request #5012 from i-c/atlantis

Add Atlantis.app v0.9.9.4