Serialization injection for transaction building

There is a request to allow for custom serialization schemes to be injected into Corda when creating new transaction objects. To achieve this, the current serialization framework needs to be extended to allow for custom schemes to be registered, and a mechanism needs to be put in place to allow such schemes to be registered and their use triggered.

This is an experimental feature and so would likely be gated behind some sort of experimental flag in the eventually shipped version.