Switch tests from zemu to ragger

[tdejoigny-ledger]

First PR to initiate the transition from Zemu framework to Ragger framework.

As soon as this PR is merged, we can :

• remove the Ethereum client from the repo
• update the test requirements file "requirement.txt" to use directly the eth client available on pypi
• update the swap test (and the CI) in order to build a known tx payload (instead of using a raw transaction from Etherscan) and to sign it (allowing the removal of flag "BYPASS_SIGNATURES=1" in ETH app)
• use the correct branch for plugin-sdk sub-module (>>develop branch)

[fbeutin-ledger]

#105