Separate qyality behavior in separate class

Same reason as for the sellIn behavior. We want to be able to provide
separate implementations and test them separately

Java/src/main/java/com/gildedrose/behavior/quality/DefaultQualityBehavior.java

@@ -0,0 +1,22 @@
+package com.gildedrose.behavior.quality;
+
+import com.gildedrose.Item;
+
+public class DefaultQualityBehavior implements QualityBehavior {
+
+    public static final int MAX_QUALITY_LEVEL = 50;
+    public static final int MIN_QUALITY_LEVEL = 0;
+
+    @Override
+    public void processQualityUpdate(Item item) {
+        decreaseQuality(item);
+    }
+
+    private void decreaseQuality(Item item) {
+        item.quality = limitQuality(item.quality - 1);
+    }
+
+    private int limitQuality(int newQuality) {
+        return Math.max(MIN_QUALITY_LEVEL, Math.min(MAX_QUALITY_LEVEL, newQuality));
+    }
+}

Java/src/main/java/com/gildedrose/behavior/quality/QualityBehavior.java

@@ -0,0 +1,8 @@
+package com.gildedrose.behavior.quality;
+
+import com.gildedrose.Item;
+
+public interface QualityBehavior {
+
+    void processQualityUpdate(Item item);
+}