Allow cephalopods to gain the ability to eat, sleep underwater

[Psithief]

Summary

Features "Allow cephalopods to gain the ability to eat, sleep underwater"

Purpose of change

I thought it was strange that fish mutants and frog mutants could eat underwater but a cephalopod mutant could not. I didn't really care about sleeping.

Describe the solution

This modifies the Aqueos Sleeper trait to also be in the Cephalopod mutation tree, requiring the threshold and the Cephalopod Gills mutation.

Describe alternatives you've considered

I considered requiring the Cephalopod Eyes mutation instead. I don't understand why this mutation requires the eye mutations and not the breathing underwater mutations.

Testing

I tested loading a game to make sure there were no JSON errors.
I tested using the debug menu to grant the mutation to a character with the THRESH_CEPHALOPOD and GILLS_CEPH mutations.

Additional context

If merged, will data/mods/extra_mut_scen/mutation_scenarios.json need to be updated as well?

[Maleclypse]

Thanks for your contribution!