#354 Added WelcomeMessage Service and Tests for tier example of featureToggle

feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/Service.java

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+package com.iluwatar.featuretoggle.pattern;
+
+import com.iluwatar.featuretoggle.user.User;
+
+/**
+ * Created by joseph on 26/01/16.
+ */
+public interface Service {
+
+    public String getWelcomeMessage(User user);
+}

feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/tieredversion/TieredFeatureToggleVersion.java

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+package com.iluwatar.featuretoggle.pattern.tieredversion;
+
+import com.iluwatar.featuretoggle.pattern.Service;
+import com.iluwatar.featuretoggle.user.User;
+import com.iluwatar.featuretoggle.user.UserGroup;
+
+/**
+ * Created by joseph on 26/01/16.
+ */
+public class TieredFeatureToggleVersion implements Service {
+
+    @Override
+    public String getWelcomeMessage(User user) {
+        if(UserGroup.isPaid(user)){
+            return "You're amazing thanks for paying for this awesome software.";
+        }
+
+        return "I suppose you can use this software.";
+    }
+
+}