EstimatedHistogram: Add constructor from data

This patch allows to create an EstimatedHistogram from an array of data
value.

It will be used by the APIClient to return EstimatedHistogram

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>

src/main/java/com/cloudius/urchin/utils/EstimatedHistogram.java

@@ -67,6 +67,12 @@ public class EstimatedHistogram {
         buckets = new AtomicLongArray(bucketData);
     }
 
+
+    public EstimatedHistogram(long[] bucketData) {
+        bucketOffsets = newOffsets(bucketData.length - 1);
+        buckets = new AtomicLongArray(bucketData);
+    }
+
     private static long[] newOffsets(int size) {
         long[] result = new long[size];
         long last = 1;