[Cashtab] Support copying full amount

Summary:
T3570

Use case so will support.

Add a copy paste icon so that user may copy the exact XEC amount sent or received in a tx.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16287