Add object (de)serialization support to cells

This adjusts the cells rpcapi to use the Object serializer class.
This also makes the cells messaging layer, which handles formatting of
cell<->cell messages, serialize objects correctly when contained as
arguments to the cells messaging methods.

Related to blueprint unified-object-model

Change-Id: Iec328827819f25a16d1fd901f4d6c896525f0bb6
Merge "Add object (de)serialization support to cells"