[Cashtab] Add support for Malaysian Ringgit

Summary:
Add support for setting foreign currency to MYR

T3562

Test Plan:
Proofread to confirm correct ticker and symbol. npm start and confirm price makes sense.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16076