Surgery Modifications

Semi-rewrites how surgery failure works.  Using an improper surface will call the surgery step's fail proc instead of just doing a melee attack.
Adds 'surgery odds' var to objs, which determines effectiveness.  The numbers for operating tables/roller beds/tables remain unchanged from the previous version, however doing it this way makes it cleaner to add new surfaces in the future.
Adds a proc to get a surgery surface.
Also makes burn repair on FBPs more efficent, so that one scorched robot does not take literally all of robotic's wires.

code/modules/tables/tables.dm

@@ -8,6 +8,7 @@
 	climbable = 1
 	layer = 2.8
 	throwpass = 1
+	surgery_odds = 66
 	var/flipped = 0
 	var/maxhealth = 10
 	var/health = 10