[cashtab] Header UI overhaul

Summary:
Proposed ui changes and code consolidation for the cashtab header.

• consolidate header code into one component
• new ui cards for xec, xecx, and firma balances with individual fiat balances
• xecx and firma info in place of 0 balances
• cleaned up wallet select, copy address and hide balances
• update tests to work with new header

new ui

old ui

Test Plan: preview the app and check the header is working right

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: alitayin, emack, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18066