Implement reviewer access via REST

This change enables users to request details about a reviewer given a
change and a reviewer id.  The returned result is a map including the
reviewers:
* kind (gerritcodereview#reviewer)
* id
* email
* name (if provided)

Example:
curl -s localhost:8080/
    changes/blah~master~I2933f24c1fc0d7f44a34bb1dc7a3242fdfd29028/
    reviewers/1000000

{
  "kind": "gerritcodereview#reviewer",
  "id": "1000000",
  "email": "cco3%40android.com"
}

Change-Id: I3e164527d5e4cc5707577b31a8618a7ae9f7b098

gerrit-server/src/main/java/com/google/gerrit/server/change/ReviewerJson.java

@@ -0,0 +1,38 @@
+// 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.server.change;
+
+import com.google.gerrit.reviewdb.client.Account;
+
+public class ReviewerJson {
+  ReviewerJson() {
+  }
+
+  public ReviewerInfo format(ReviewerResource reviewerResource) {
+    ReviewerInfo reviewerInfo = new ReviewerInfo();
+    Account account = reviewerResource.getAccount();
+    reviewerInfo.id = account.getId().toString();
+    reviewerInfo.email = account.getPreferredEmail();
+    reviewerInfo.name = account.getFullName();
+    return reviewerInfo;
+  }
+
+  public static class ReviewerInfo {
+    final String kind = "gerritcodereview#reviewer";
+    String id;
+    String email;
+    String name;
+  }
+}