Projectiles reorganization and cleanup, impact effects, subtle EMP tweaks (#6741)

No gameplay changes except for EMP rebalancing.

Emps are now deterministic
Ion rifles now always hit for strength 2 instead of a probability tree
of strengths
EMP damage slightly lessened as this makes a lot of things guaranteed to
hit with strength 2 instead of 3

code/modules/modular_computers/computers/modular_computer/damage.dm

@@ -44,7 +44,8 @@
 /// EMPs are similar to explosions, but don't cause physical damage to the casing. Instead they screw up the components
 /obj/item/modular_computer/emp_act(severity)
 	. = ..()
-	take_damage_legacy(rand(100,200) / severity, 50 / severity, 0)
+	spawn(-1)
+		take_damage_legacy(rand(100,200) / severity, 50 / severity, 0)
 
 /**
  * "Stun" weapons can cause minor damage to components (short-circuits?)