[alias-server] [p5] Commenced getAliases function

Summary:
T2922

Depends on D13012

Commenced implementation of getAliases function, to match the same functionality of Cashtab. Because the function is complex and requires helper functions, breaking it into parts. This diff parses the first registered alias tx.

Test Plan:
cp config.sample.js config.js
node index.js

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D13078