Enable inter server endpoint communication in a compatibility mode

Enable a compatibility mode that allows 3 main servers (Hot Rod, Memcached, REST ) and embedded mode (in-VM) to interact with each other. This would require some compatibility mode.

Obviously, this needs to be testable, so possibly adding tests to the 'integration-tests' module. Need to demonstrate storing data in one “client” and accessing from others, modifying in others, and re-accessing in the first. Test should cover each of the 4 “clients” as the initial creator.

When running in this mode, keys to be stored as Strings. In the case of REST and memcached, keys are strings anyway. In the case of Hot Rod, start the server with a flag to determine the encoding used (assuming the HR client uses Strings as well).

For values - polymorphism between a MarshalledValue (in-VM), MemcachedValue, HotRodValue, RESTValue. Lazily convert from one to the other. May need a PortableValue as well, which contains all of the metadata of all of the value types above.

May need to provide and encoding for values as well - to be able to make sense between Hot Rod byte array values and Strings in REST/memcached (base64?).

In-VM may need registration of an Externalizer?