Added support to access Hbase over REST

Modified HBaseTemplate to support accessing HBase over REST by wrapping HBase rest client (http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/rest/client/package-summary.html). This is useful in environments where HBase is not directly accessible through Zookeeper and needs to be accessed over HTTP/REST. Changes are backward compatible and should not effect existing behavior.