New system for CO2 asphixyation

Too much CO2 now makes you slowly gain oxyloss instead of making you
fall unconscious immediately and quickly killing you after 30 seconds.

Conflicts:
	code/modules/mob/living/carbon/human/life.dm
Completed unfinished species.breath_type switch

Conflicts:
	code/modules/mob/living/carbon/human/life.dm
Adjusts co2 warning frequencies
Fixes missing 'else'

Conflicts:
	code/modules/mob/living/carbon/human/life.dm
C02 -> carbon_dioxide

Renamed carbon dioxide breathing type string to hopefully prevent
confusion in the future.

Conflicts:
	code/modules/mob/living/carbon/human/life.dm
	code/modules/mob/living/carbon/species.dm