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.
I would suggest:

M.visible_message("<span class='notice'>[M] shakes [src] trying to wake [t_him] up!</span>", \
                               "<span class='notice'>You shake [src], but \he just won't wake up! Probably suffering from SSD.</span>")
```
No need to strain the immershuns of everyone watching with SSD reminders.