New Consensus: Tree State Transaction Handling <> Code Duplication

With the new introduced tree state for the new consensus protocol a great deal of duplicated code (which basically shares the same implementations used in the persistent tree state) has been introduced with respect to transaction handling.

See https://github.com/Concordium/concordium-node/pull/708

This is not ideal and incurs a non insignificant maintenance burden and so we should refactor this in order to make the future maintenance more approachable.