[Cashtab] Add support for New Taiwan Dollar

Summary: Added support for New Taiwan Dollar. Related to task T2012.

Test Plan:
npm start
cd web/cashtab
navigate to configure page
select New Taiwan Dollar in the Fiat Currency dropdown
ensure fiat is set to New Taiwan Dollar & that conversion is taking place

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10581