Allow the ethereum light client to prove the state of all contracts

[srdtrk]

Summary

Currently, our ethereum light client can only prove the state of a single contract in a single mapping slot. We always target the ICS26Router's commitments mapping. This feature would move all account proofs to membership entry point.

Problem Definition

This would make our the client more compliant with the IBC and sync-protocol specs and clean up our light client header. Also, this would allow more use cases since we would be able to prove the state of other contracts in eth.

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