ONOS-542 Defining application subsystem interfaces & public constructs.

Change-Id: Iba0d2cb69dace5beee8a68def9918059ce755b5c
diff --git a/core/api/src/main/java/org/onosproject/app/ApplicationListener.java b/core/api/src/main/java/org/onosproject/app/ApplicationListener.java
new file mode 100644
index 0000000..7a68057
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/app/ApplicationListener.java
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.app;
+
+import org.onosproject.event.EventListener;
+
+/**
+ * Entity capable of receiving application related events.
+ */
+public interface ApplicationListener extends EventListener<ApplicationEvent> {
+}