Resolve forks created by different transactions updating the same account

[PhilippGackstatter]

Resolve forks created by different transactions updating the same account.

If we have two batches that update the same account from the same initial state A but one batch updates it to B and another updates it to C, then this is a fork in the account state.
Currently, the block kernel errors in this scenario but eventually we should resolve the conflict and choose one of the transaction chains that is accepted as the new state.

Reference:

At some point in the future, we may need to resolve such conflicts differently. That is, if there is a conflict, we'd drop one of the transaction chains (e.g., the transaction which resulted in A -> F and all of its descendants). This won't happen until we have decentralized batch production, but still let's create an issue for this.

From: #1123 (comment)