Adding api wrappers for getting comments.

Pulling the Side enum into com.google.gerrit.common so that it's shared
across the server and the client.

Change-Id: I4d4e8b74dd2adcebc44e403a1cbf4352d05762fb

gerrit-common/src/main/java/com/google/gerrit/common/changes/Side.java

@@ -0,0 +1,20 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// 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 com.google.gerrit.common.changes;
+
+/** The side on which a comment was added. */
+public enum Side {
+  PARENT, REVISION;
+}