Account Redesign PoC 2

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Vitalik's new design

A two-layer account trie inside a single-layer trie

Implementation Plan

1. Replace trie.py with new_bintrie.py
2. Update the State and Account class
3. Integrate with stateless_client.py

[hwwhww]

Regarding (2), remove the Account class, as theoretically we don't even need it. The reason is that with the re-write, there's no place where an account is loaded in its entirety, it's always each individual piece of an account that gets loaded separately.

[hwwhww]

Close all old stuff