Upgrade Kafka 0.7=>0.8 refactor kafka operators #73

Squashed commit of the following:

commit aec226096d9d9653434805d78ee21ee008bfd41c
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Tue Oct 1 11:16:50 2013 -0700

    last commit

commit 454ceff30178d095ec9b48bfa1682b47cc77d924
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Mon Sep 30 18:25:19 2013 -0700

    clean AbstractKafkaInputOperator #73

commit 9cb6f4e118de1496ce3c6cef22922e1950a2e264
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Mon Sep 30 17:41:26 2013 -0700

    Refactor Kafka Input Operator make code more clean and api easy to use #73

commit ab5c792f4d860bd8aed3083a4447e61cd12abcbb
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Mon Sep 30 10:33:22 2013 -0700

    Removing timing issue in KafkaOutputOperatorTest
    Modify the dependency in pom.xml

commit 77e76588829208f2f028c61f74b87c860a445d62
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Thu Sep 26 13:22:59 2013 -0700

    Format and comment refinement #73

commit 3f3eb55dce23fd97a6f8fccce98ed755bcf21d76
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Thu Sep 26 11:44:51 2013 -0700

    Update the kafka to 0.8 #73