[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/core/common/src/main/java/org/onosproject/codec/impl/CodecManager.java b/core/common/src/main/java/org/onosproject/codec/impl/CodecManager.java
index e9fc7ac..d68b287 100644
--- a/core/common/src/main/java/org/onosproject/codec/impl/CodecManager.java
+++ b/core/common/src/main/java/org/onosproject/codec/impl/CodecManager.java
@@ -17,7 +17,6 @@
 
 import com.codahale.metrics.Metric;
 import com.google.common.collect.ImmutableSet;
-
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
 import org.apache.felix.scr.annotations.Deactivate;
@@ -35,11 +34,11 @@
 import org.onosproject.net.Link;
 import org.onosproject.net.Path;
 import org.onosproject.net.Port;
+import org.onosproject.net.device.PortStatistics;
 import org.onosproject.net.driver.Driver;
 import org.onosproject.net.flow.FlowEntry;
 import org.onosproject.net.flow.FlowRule;
 import org.onosproject.net.flow.TableStatisticsEntry;
-import org.onosproject.net.device.PortStatistics;
 import org.onosproject.net.flow.TrafficSelector;
 import org.onosproject.net.flow.TrafficTreatment;
 import org.onosproject.net.flow.criteria.Criterion;