SSD mechanic rewrite

Removed logging out/DCing from automatically putting people to sleep.

Removes the immune to SSD variable and instead replaces it with the player_logged variable. Allowing more flexibility with SSD code and effects without having to put in exceptions.

Implemented checks for player_logged variable in carbon/human to make SSD crewmembers fall asleep, stay asleep and a different result when someone tries to shake them awake.

At this moment in time, player_logged does not do anything else for non-carbon/human mobs but changes number, might implement a power saving standby mode or similar in the future.

Still trying to figure out how to squash commits to be less spammy, my apologies.
The span needs closed here, and the wording is a bit stilted.  "[...]but they do not respond... maybe they have S.S.D.?"  maybe?