Adding serialization module

at the moment, the new module contains only a MultiClassSerializationHelper which can be used to serialize objects into byte arrays and vice versa.
The type parameter can be used if one helper is used for objects with the same parent type only. Otherwise the serialize-Method must expect an Object and the deserialize-Method will return an instance of type Object. I thought it would be easier to use if one can restrict this to a specific type when using an instance of this class only for a specific type (e.g. MessageLite in the testbed-runtime case).