Allow Cpp client to read proto object written by the java client

Now that the server uses a protoschema, it is very nice to support the following scenario:

• users writes a Person object (defined with proto) with the java client
• the cpp client can read the same Person object

Right now, the java client uses protostrem to encode the object type in a custom way. This "custom encoding" should be hidden into an helper class in the cpp client so that it is not exposed directly to the user (please sync up with anistor to get the exact encoding).

So the result of this JIRA should be:

• providing such an encoder for the cpp client
• testing that a Person object written by java is actually correctly read by the CPP client
• documenting the usage this scenario together with the CPP documentation, i.e. the compatibility between the cpp and the java client

Please ask anistor for details on the interoperability.