Change `access_list` type

[gurukamath]

          Is there a more natural way to represent these? Maybe something like:

access_list: Dict[Address, Set[Bytes32]]

Originally posted by @SamWilsn in #1131 (comment)

[Shashwat-Nautiyal]

Hello @gurukamath, please review PR #1148 whether it meets the requirement?

[gurukamath]

Closing this in favor of #947