Sort approvals in REST endpoints and approval table

Document REST endpoints to return approvals within a given list by
timestamp, although the timestamp is not exposed. Sort labels by
corresponding ApprovalCategory position.

On the client side, sort users by the owner first, followed by users
with nonzero votes.

Change-Id: I68cd21e4a62b76bd7de2bf1dd1e18e8675dd34db

gerrit-common/src/main/java/com/google/gerrit/common/data/ApprovalDetail.java

@@ -18,6 +18,7 @@ import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 
 import java.util.ArrayList;
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -25,6 +26,13 @@ import java.util.Map;
 import java.util.Set;
 
 public class ApprovalDetail {
+  public static final Comparator<ApprovalDetail> SORT =
+      new Comparator<ApprovalDetail>() {
+        public int compare(ApprovalDetail o1, ApprovalDetail o2) {
+          return o1.hasNonZero - o2.hasNonZero;
+        }
+      };
+
   protected Account.Id account;
   protected List<PatchSetApproval> approvals;
   protected boolean canRemove;
@@ -33,6 +41,7 @@ public class ApprovalDetail {
   private transient Set<String> approved;
   private transient Set<String> rejected;
   private transient Map<String, Integer> values;
+  private transient int hasNonZero;
 
   protected ApprovalDetail() {
   }
@@ -59,6 +68,7 @@ public class ApprovalDetail {
       approved = new HashSet<String>();
     }
     approved.add(label);
+    hasNonZero = 1;
   }
 
   public void rejected(String label) {
@@ -66,6 +76,7 @@ public class ApprovalDetail {
       rejected = new HashSet<String>();
     }
     rejected.add(label);
+    hasNonZero = 1;
   }
 
   public void votable(String label) {
@@ -80,6 +91,9 @@ public class ApprovalDetail {
       values = new HashMap<String, Integer>();
     }
     values.put(label, value);
+    if (value != 0) {
+      hasNonZero = 1;
+    }
   }
 
   public boolean isApproved(String label) {