REST API: Replicator read & write file

Change-Id: If807902e12c17172de14322c63a04d0fc7aa51ca
Reviewed-on: http://naan.mimuw.edu.pl:8001/113
Tested-by: Nebulostore Nebulostore <nebulostore@gmail.com>
Reviewed-by: Bolek Kulbabinski <bkulbabinski@gmail.com>