[ONOS-3603] Implement REST API for Group query, insert, delete

* Implement decoding feature for GroupBucketCodec and GroupCodec
* Implement GroupsWebResource
* Add unit test for GroupBucketCodec and GroupCodec
* Add unit test for GroupsWebResource
* Add group insertion json example
* Add Swagger doc

Change-Id: Ie58cba2e1af996c7b8652a55d9ef0c27207beafc
diff --git a/web/api/src/test/resources/org/onosproject/rest/post-group.json b/web/api/src/test/resources/org/onosproject/rest/post-group.json
new file mode 100644
index 0000000..675f244
--- /dev/null
+++ b/web/api/src/test/resources/org/onosproject/rest/post-group.json
@@ -0,0 +1,18 @@
+{
+  "type": "ALL",
+  "deviceId": "of:0000000000000001",
+  "appCookie": "1",
+  "groupId": "1",
+  "buckets": [
+    {
+      "treatment": {
+        "instructions": [
+          {
+            "type": "OUTPUT",
+            "port": 2
+          }
+        ]
+      }
+    }
+  ]
+}
\ No newline at end of file