Replace pycrypto with pycryptodome

[erickearns]

Using ledgerblue in coordination with various Ethereum tools (e.g. https://github.com/ethereum/web3.py/blob/master/setup.py#L27) is problematic as pycryptodome has replaced pycrypto in most modern tool dependency trees. As pycryptodome is largely a drop-in replacement for pycrypto, updating this dependency would solve a significant amount of headache.

[redshiftzero]

Heads up, we made this same change in SecureDrop, replacing pycrypto with pycryptodome (ref: freedomofpress/securedrop#2903). However, since we did that we were strongly advised for security reasons to move away from pycryptodome to pyca/cryptography (refs: PyCQA/bandit#307, freedomofpress/securedrop#3399, freedomofpress/securedrop#3458). If using audited crypto libraries is important for this project, you may want to do the same, though I understand that this may be significantly more work.