added http get operator

Squashed commit of the following:

commit f1af83c92b431b7b9da7054a928b5a6b7392b692
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Thu May 15 11:46:24 2014 -0700

    clean up

commit d66ce22bea481fa2f9d721828b3a3296e0960d28
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Thu May 15 11:34:17 2014 -0700

    added http get operator with map input port for query parameters

commit 91b3895769f6b4476e8fe88a233bb746f15fc06d
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Mon May 12 19:16:33 2014 -0700

    clean up

commit 9c108cd370d695d540dad2fddd9b520bbc840248
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Mon May 12 19:06:15 2014 -0700

    renamed HttpOutputOperatorTest to HttpPostOutputOperatorTest

commit 173be15c017eff53fd426efadac6091169f5c926
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Mon May 12 18:44:41 2014 -0700

    changed method call to set the url

commit c07d4b5c077405bbb1406f8be03f0ebdf852ce2a
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Mon May 12 18:44:03 2014 -0700

    added HttpGetOperator to send get requests and process responses if output port is connected

commit 6620a1f3f730e936c3645e74411a89fb34cb1d30
Author: Ashwin Chandra Putta <ashwin@datatorrent.com>
Date:   Mon May 12 18:43:15 2014 -0700

    added abstract http operator and renamed HttpOutputOperator to HttpPostOutputOperator