Overdose Change, Reagent Tweaks and Fixes, IPC Damage Fixes

Adjusts how Overdosing works
- Overdose effects now stop if you have less than the overdose threshold
for the given reagent in your system
- Previously, overdose effects would continue until all of the reagent
was removed from the body
- After dropping below the overdose threshold, reagents will process as
normal as long as they do not surpass the threshold again.

Tweaked some Synthetic-oriented reagents
- Synthetic drugs no longer will cause Toxins damage
- The toxins damage for these has been replaced with either another form
of damage or side-effect
- Degreaser no longer cures Toxins Damage in Synthetics
- Degreaser still acts as a chemical purgative and lube cleaner, but
helps cure certain side-effects much like Coffee does for organics.

Sterlizine recipe changed to require antihol and chlorine
- Effectively the same as the old recipe, except actually mixable
- Fixes #2030

Increases max_damage of MMI Holders to 200 (from 60)
- Now matches the max_damage for organic brains
- Should make IPC brain damage more consistent with organic brain damage

Gives IPCs the NO_POISON flag
- This should make IPCs immune to toxins damage again, as intended
originally.
- Fixes #2151.

code/modules/mob/living/carbon/human/species/station.dm

@@ -499,7 +499,7 @@
 
 	passive_temp_gain = 10 //this should cause IPCs to stabilize at ~80 C in a 20 C environment.
 
-	flags = IS_WHITELISTED | NO_BREATHE | NO_SCAN | NO_BLOOD | NO_PAIN | NO_DNA_RAD
+	flags = IS_WHITELISTED | NO_BREATHE | NO_SCAN | NO_BLOOD | NO_PAIN | NO_DNA_RAD | NO_POISON
 	clothing_flags = HAS_SOCKS
 	bodyflags = HAS_SKIN_COLOR
 	dietflags = 0		//IPCs can't eat, so no diet