[Cashtab] Show token info on Send Token screen

Summary:
Fetch additional token info from API when the user navigates to the Send Token screen.

If the API call fails, render the token info already saved in wallet state. The info panel is only rendered if the API call returns a validated object. Unit tests are added for validation.

Test Plan: npm start, go to the send token screen, check out the stats

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9496