[Cashtab] [BCH deprecation] Pt 1/2 - Implement local toHash160 logic

Summary:
T2730

As a prerequisite to deprecating BCH.Address.toHash160(), this diff implements a local swiss army knife version of toHash160() that converts ecash, etoken, bitcoincash and simpleledger addresses to hash160.

Relies on the bs58 library (6KB).

Test Plan:

• npm install or npm i bs58
• npm test and ensure all toHash160 unit tests pass
• npm start
• send a private message to another address and observe the 'getRecipientPublicKey(): recipientAddressHash160 matches localRecipientAddressHash160' console log message
• create a new wallet and observe the 'deriveAccount(): hash160 matches localhash160' console log message'
• send a private message using the new wallet and observe the 'getRecipientPublicKey(): recipientAddressHash160 matches localRecipientAddressHash160' console log message

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D12395