Introduce hash of account storage

[zavodil]

We have a code_hash which is extremely useful to recognise current application code for the given account.
Could you introduce a similar hash to determine account storage (data)?

Right now we have a continuous bug when 2FA is trying to overwrite account state and makes account invalid. We can't recognise if account has existing state using code_hash only.

Same approach may be used to verify if account state was modified (could be useful for many apps).

[bowenwang1996]

This would be much easier to do if we have account state in its own trie.