[Cashtab] Add space before ticker in tx history

Summary: T1740

Test Plan: npm start and observe that there is a space in between amount sent or received and the XEC ticker in the tx history panel, e.g. - 100 000 XEC instead of - 100 000XEC

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9907