TE Topoplogy subsystem I2RS API changes

This submission contains the following:

1. Major changes in apps/tetopology. The changes are mainly introduced
   to support new searching keys in TE Topology.

2. Add RESTCONF notification support in the TE Provider. i.e., for
   south-bound RESTCONF communication with the domain controller.

Change-Id: I6786959deb66c98626edc65ff52694dcf08981a3
diff --git a/apps/tetopology/api/src/main/java/org/onosproject/tetopology/management/api/link/ExternalLink.java b/apps/tetopology/api/src/main/java/org/onosproject/tetopology/management/api/link/ExternalLink.java
new file mode 100644
index 0000000..9e11152
--- /dev/null
+++ b/apps/tetopology/api/src/main/java/org/onosproject/tetopology/management/api/link/ExternalLink.java
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2016 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.tetopology.management.api.link;
+
+import com.google.common.base.MoreObjects;
+import com.google.common.base.Objects;
+
+/**
+ * Representation of an external domain link.
+ */
+public class ExternalLink {
+    private final TeLinkTpGlobalKey externalLinkKey;
+    private final Long plugId;
+
+    /**
+     * Creates an instance of an external domain link.
+     *
+     * @param externalLinkKey external TE link key
+     * @param plugId          global plug identifier
+     */
+    public ExternalLink(TeLinkTpGlobalKey externalLinkKey, long plugId) {
+        this.externalLinkKey = externalLinkKey;
+        this.plugId = plugId;
+    }
+
+    /**
+     * Returns the external TE link key.
+     *
+     * @return the externalLinkKey
+     */
+    public TeLinkTpGlobalKey externalLinkKey() {
+        return externalLinkKey;
+    }
+
+    /**
+     * Returns the global plug identifier.
+     *
+     * @return value of the global plug id
+     */
+    public Long plugId() {
+        return plugId;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(externalLinkKey, plugId);
+    }
+
+    @Override
+    public boolean equals(Object object) {
+        if (this == object) {
+            return true;
+        }
+        if (object instanceof ExternalLink) {
+            ExternalLink that = (ExternalLink) object;
+            return Objects.equal(externalLinkKey, that.externalLinkKey) &&
+                    Objects.equal(plugId, that.plugId);
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(this)
+                .add("externalLinkKey", externalLinkKey)
+                .add("plugId", plugId)
+                .toString();
+    }
+}