Add iterative dynamo queries and scans

Hello @x-ma, 

Please review the following commits I made in branch 'nick-next'.

4a8257df5269a92eb69ac7526827cf35c9fdf0e5 (2013-11-25 12:42:33 -0500)
Add iterative dynamo queries and scans

f78aee3b0e1eb01f718b2700b3f89fb7b936d4eb (2013-11-25 12:15:39 -0500)
Move DynamoResponse into a separate class.

R=@x-ma