Adds a Trait system (#4048)

* Works on trait system, wip.

* Finalizes traits.
Fixes a few bugs with medical machines assuming a max health of 100.

code/modules/reagents/Chemistry-Reagents.dm

@@ -63,7 +63,13 @@
 		return
 	var/removed = metabolism
 	if(!mrate_static == TRUE)
+		// Modifiers
+		for(var/datum/modifier/mod in M.modifiers)
+			if(!isnull(mod.metabolism_percent))
+				removed *= mod.metabolism_percent
+		// Species
 		removed *= M.species.metabolic_rate
+
 	if(ingest_met && (location == CHEM_INGEST))
 		removed = ingest_met
 	if(touch_met && (location == CHEM_TOUCH))