Refactor testnet to easily replace Tendermint by Tendermock

[hvanz]

This is for preparing Atomkraft before integrating Tendermock. Once Tendermock is ready, we may still want to use in some ocassions the chain binary with Tendermint. We need to identify and isolate the code that connects to Tendermint/Tendermock to be able to easily replace one by the other. It could be in a new module/class with the methods that call Tendermint/Tendermock, such as initialize node and broadcast tx.