Guarantee Backward Compatibility for Grafts, Protocol and Gateways

With first stable release we will switch to backward compatible releases plan so every new Grafting engine will support old versions of Gateways (starting with first stable release), all changes to Hypertube will ensure backward compatibility with older version of calling side as well as compatibility of SDK exposed to Graft with previous hypertube versions so every existing Graft can be safely used with any future release of Hypertube.