[Cashtab] Get token info from cache in airdrop calc screen

Summary:
Every time we need token info that can be cached, we should get it from the cache. If it is not from the cache, we add it to the cache.

The airdrop calculator is still getting this info manually.

Implement standardized Cashtab practice.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15969