[ABW]: [NIP] Added logging for validate_invariants

#20 (closed) Added summary at the end of successful validate_invariants call

Note that since the only translation of asset to string present in chain code looks weird I decided to use raw amount when printing total balances - the readers of the log should have no trouble interpreting it.

The code of validate_invariants didn't change much recently and all additions related to delayed_voting are done correctly. There is one thing I don't like though: account_object::get_real_vesting_shares contains assertion that has no place in the getter in my opinion. For now we have to let it be, but it really should only be in setter (once we start making members of chain objects private).