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.
Completed unfinished species.breath_type switch
Adjusts co2 warning frequencies
Fixes missing 'else'
C02 -> carbon_dioxide

Renamed carbon dioxide breathing type string to hopefully prevent
confusion in the future.
Merge pull request #5083 from mwerezak/co2

New System for CO2 Asphixyation