T2370

As a prerequisite to deprecating the use of BCH.SLP.Address.toLegacyAddress in useWallet and cashMethods, this diff replicates this logic.

The bchaddrjs-slp library (659 kb) is used to convert legacy cash addresses to legacy (bitcoin) address before feeding them into the OP RETURN script generation process. This conversion is not supported by the ecashaddrjs library hence the need for this additional library.

npm install or npm i bchaddrjs-slp
npm test and ensure existing unit test suite passes
npm start
send a token with an OP_RETURN msg and observe the 'toLegacyAddress output from BCH-js matches bchaddrs-slp' console log message
burn a token and observe the same console log message
create a new wallet to trigger useWallet.deriveAccount() and observe the same console log message