[AETHER-76] Complete T3 offline mode

- For the performance improvement, T3 offline mode uses snapshots of the network states
called Network Information Base (NIB) instead of runtime interactions with ONOS core
during troubleshooting a Trellis system.
- Enables NIB to be manually filled with the followings via T3-load commands.
  - Static dump files of onos-diagnostics (t3-load-file).
  - Returns of API calls to live ONOS stores (t3-load-snapshot).
- Enables NIB to be auto-filled with live ONOS stores.
  - When T3-execution commands (e.g. pingall) found NIB is invalid.
- Partially tested with some mininet topos for Trellis
(https://github.com/opennetworkinglab/routing/tree/master/trellis).
- Usage instruction docs (https://docs.trellisfabric.org/troubleshooting.html).

Change-Id: I2bb546bdde454a034338cd896388fa0b37d868be
(cherry picked from commit c3803e7fad5fb28ecf3e83253f183a34936be4a0)
diff --git a/app/src/main/java/org/onosproject/t3/api/NibProfile.java b/app/src/main/java/org/onosproject/t3/api/NibProfile.java
new file mode 100644
index 0000000..146d98a
--- /dev/null
+++ b/app/src/main/java/org/onosproject/t3/api/NibProfile.java
@@ -0,0 +1,74 @@
+/*
+ * Copyright 2020-present Open Networking Foundation
+ *
+ * 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.t3.api;
+
+import java.text.SimpleDateFormat;
+
+/**
+ * Basic descriptions about a single Network information Base (NIB) instance.
+ */
+public class NibProfile {
+    // default false means the contents of this NIB are empty at the instantiation
+    private boolean valid = false;
+    private String date;
+    private SourceType sourceType;
+
+    public enum SourceType {
+        /**
+         * Provided by dump files.
+         */
+        FILE,
+        /**
+         * Provided by a running system.
+         */
+        SNAPSHOT
+    }
+
+    public NibProfile(long date, SourceType sourceType) {
+        this.valid = true;
+        this.date = new SimpleDateFormat("dd-MM-yyyy hh:mm").format(date);
+        this.sourceType = sourceType;
+    }
+
+    /**
+     * Returns the validity state of this NIB.
+     *
+     * @return true once this profile is initialized
+     */
+    public boolean isValid() {
+        return valid;
+    }
+
+    /**
+     * Returns the time this NIB has been filled.
+     *
+     * @return string representation for the time
+     */
+    public String date() {
+        return date;
+    }
+
+    /**
+     * Returns the type of the source used to fill this NIB.
+     *
+     * @return source type
+     */
+    public SourceType sourceType() {
+        return sourceType;
+    }
+
+}