Simplify AccountDetails in ProvenTransaction

[bobbinth]

As noted by @hackaugusto in #485 (comment), we may be able to simplify AccountDetails in the ProvenTransaction struct to carry just account delta (even in the case of new accounts).

[polydez]

@bobbinth @hackaugusto
One thing we've missed: Account also contains account's code, but we don't have such analogue in AccountDelta. In our previous design, we was able to deploy code once and then update other data, so if we add this field to AccountDelta, it will be useless for updates in existing accounts. Do we have another approach of account's code deployment?

[bobbinth]

The proper way to handle it is to add account code updates to AccountDelta as well. But this is quite a bit of work and I'm not sure we should dedicate time to this now.

So, I'm thinking we just put #530 on hold for now and come back to it later.

[polydez]

We decided to not keep only delta, because this makes code even worse due to additional cases to check: #530 (comment)