map setting refund (#1709)

core/src/mindustry/game/Rules.java

@@ -44,6 +44,8 @@ public class Rules{
     public float buildCostMultiplier = 1f;
     /** Multiplier for building speed. */
     public float buildSpeedMultiplier = 1f;
+    /** Multiplier for percentage of materials refunded when deconstructing */
+    public float deconstructRefundMultiplier = 0.5f;
     /** No-build zone around enemy core radius. */
     public float enemyCoreBuildRadius = 400f;
     /** Radius around enemy wave drop zones.*/