Backend Sync: Adding Deferred support

Signed-off-by: José Luis Di Biase <josx@interorganic.com.ar>
Passing error on deferred request instead resp

Signed-off-by: José Luis Di Biase <josx@interorganic.com.ar>
Merge pull request #54 from inaes-tic/deferred

Backend Sync: Adding Deferred support