[Cashtab] Match UI locking pattern of rest of app in Tokens.js

Summary:
T1741

This diff extends the pattern of passing loading status to the App.js component used in D9872 to the Tokens.js screen.

In addition, there was a bug on token creation where the loading status did not clear after successful token mints. This is patched.

An artifact comment is also removed.

Test Plan: npm start, navigate to Tokens, create a token, notice that full UI locks while mint tx is being broadcast, notice that full UI is unlocked after tx is complete.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9888