Backwards compatibility with v4 nodes

[amangale]

The use of CurrencyValue will make the listings upgrade to v5. The scenario where an upgraded (or v5) node wants to buy from a v4 node is quite possible. In this case, the network messages (specific to ordering) would fail because the current network messages are tightly coupled with protobuf messages. Can the network service be modified in v5 such that any v5 node can still work with a v4 node wrt ordering. This would avoid the immediate mandatory upgradation of existing v4 nodes which is highly desirable from a UX perspective.