added http get operator and abstract http operator

Squashed commit of the following:

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