Added a serialization wrapper template SerializableSigOpT<>. This, and its base class, provides a generic interface to the scheduler for distributed bridges so that it can serialize SigOps without knowing their explicit type. SerializableSigOpT<> and its base class (SerializableSigOpBaseT<>) uses a regular virtual base construct, with virtual methods, to handle the separation between scheduling a generic SigOp and its associated type-specific serialization/deserialization. This virtula base-class solution has been chosen after some major efforts trying to solve the same problem (generic base interface calling a type-specific serialization) using templates only. A template-based solution woul remove the need for virtual methods, vtables, etc. But, after several unseccfull attempts, virtual base class interface is chosen in the name of progress.