MAHOUT-1493 Port Naive Bayes to Scala DSL 

Created this PR to review the patch provided by Christoph Viebig and team, Students of TU, Berlin.  It is based on Sebastian's code from before the DSL was abstracted away from Spark. 
Please try this patch:

diff --git a/h2o/src/main/java/org/apache/mahout/h2obindings/H2OHelper.java b/h2o/src/main/java/org/apache/mahout/h2obindings/H2OHelper.java
index 294ec7e..c3b1339 100644
--- a/h2o/src/main/java/org/apache/mahout/h2obindings/H2OHelper.java
+++ b/h2o/src/main/java/org/apache/mahout/h2obindings/H2OHelper.java
@@ -329,7 +329,7 @@ public class H2OHelper {
       Map<Integer,String> rmap = reverseMap(map);
 
       for (long r = 0; r < m.rowSize(); r++) {
-        writer.set(r, rmap.get(r));
+        labels.chunkForRow(r).set(r, rmap.get(r));
       }
 
       writer.close(closer);