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.
Update GURPS Character Sheet.app to v1.0.4

GCS updated and the old download link is dead, so the cask needs to be updated
to the new version.
added fenix
Merge pull request #5012 from i-c/atlantis

Add Atlantis.app v0.9.9.4
Merge pull request #5013 from vitorgalvao/add-fenix

added fenix
Merge pull request #5016 from i-c/gurps-character-sheet

Update GURPS Character Sheet.app to v1.0.4