Add support for state tests

[anvacaru]

• The new state tests change the way transactions are loaded from a JSON dict instead of an RLP-encoded bytes object. But the biggest inconvenience is that instead of v, r, and s values, they provide the sender address and the PK used to sign the transaction. To support these tests, I added a new <sender> to the <message> cells. I adapted the load and check driver.md rules to support the new JSON structure.
• Some of the check fields are currently skipped due to various reasons: (SetItem("hash") SetItem("logs") SetItem("txbytes") SetItem("indexes")); hash, for example, should check the stateRoot. However, the stateRoot is not updated by evm when running a tx.
• The transaction type is not present in the json fixture, so a temporary solution is to identify the type based on the fields identified in the transaction data. Needed to implement an additional inKeys for JSON sort in json-rpc.md.