Cuts /disease variables from 28 to 23 (includes new ones)
a disease may now have more than one spread type
added "infectivity" variable which replaces a prob(65), defaults to 65
affected_species is now viable_mobtypes, and lists typepaths, this is due to us actually having a species system now so it's confusing
adds defines for a bunch of stuff
Merge branch 'master' of https://github.com/tgstation/-tg-station into DiseaseRework

Conflicts:
	code/game/machinery/bots/medbot.dm
Merge branch 'master' of https://github.com/tgstation/-tg-station into DiseaseRework

Conflicts:
	code/modules/mob/living/carbon/carbon.dm
	code/modules/mob/living/carbon/human/human_attackpaw.dm
	code/modules/mob/living/carbon/monkey/monkey.dm
more conflict fixes.
Remembers to remove code/datums/disease.dm , code/datums/disease/_disease.dm replace it.
Merge pull request #5545 from RemieRichards/DiseaseRework

Disease Code Partial Rework