Fix BlockCapturer Handling of Contract Creation

[DavePearce]

The BlockCapturer is not always handling contract creation correctly. I believe this is the sequence where it fails:

• Constract is created
• Contract state is modified in some way

Then, the block capturer adds the account being created to the initial set of accounts in the conflation, along with storage values for the locations assigned (where each location is assigned 0x0 because it didn't exist before the conflation). This then results in BESU thinking the contract already exists at creation time, leading to a failure.