Implement a Loom Truffle provider that auto-maps accounts

[enlight]

To simplify testing and deployment on Loom we should implement another version of Loom Truffle provider that primarily operates using Ethereum accounts, rather than Loom accounts. It should be possible to create the provider using a mnemonic, and the provider will auto-map Ethereum & Loom accounts generated from that mnemonic (unless a mapping already exists for the Ethereum account, in which case it'll use the existing mapping).

In terms of implementation there's going to be a new provider class that will have a constructor that accepts a Truffle Provider instance (which will be created using the @truffle/hdwallet-provider package), the new provider will handle the account mapping and will delegate everything else to the HDWallet provider.