As per T2155, moved opReturnMsg string conversion logic from Tx.js to parseTxData in useBCH.js

npm start
test with an outbound normal message with a single recipient tx and message label shows cashtab message
test with an outbound normal message with a multi recipient tx and message label shows cashtab message
test with an outbound encrypted message with a single recipient tx and message label shows cashtab message
test with an inbound normal message from electrum with a single recipient tx and message label shows external message
test an outbound long message
test an outbound message with special symbols
ensure correct styling for encrypted and unencrypted messages