Enable having multiple test users/wallets open at once with Trireme Test Env

[MitchTurner]

So, currently, Trireme supports having multiple wallets to represent multiple actors in hand testing CLIs. So you can set up a contract with Alice, switch to Bob, and interact with the contract.

The problem is that Trireme only allows one to be active at once, through the configuration. It would be nice to be able to have two open in separate terminals. It would be much easier to jump back and forth.