[Cashtab] Fix bugs in parseChronikTx

Summary:
T3434

Instead of converting all strings (and buffers) to string at the end, just convert the buffers to string. Some buffers may require non-utf8 conversion later. Also, now that we are handling unrecognized lokad ids by separating the pushes with a space, we need to convert these strings individually.

Ignore op return "msgs" in etoken txs.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15607