Resolve "condenser_api asset inconsistency"

Closes #540 (closed)

This MR fixes incorrect hf26-serialization of data returned by condenser api's methods list_rc_accounts & find_rc_accounts.
Additionally for some other methods serializer_wrapper were modified to wrap whole containers instead of their elements which resulted in simpler & cleaner code.
A review of return types of all methods of condenser api showed that none other needs serialization fixing.

Corresponding MR in schemas - schemas!50 (merged)

UPDATE:
A commit containing related test fix has been cherry-picked on request mentioned in comments below.