[Cashtab] p8 of 8 for improved utxo mgmt

Summary:
T1683

This diff reduces the refresh rate of Cashtab by 90%. The 10s refresh rate was necessary to support the expensive API call to get eToken info for all utxos.

After the previous series of diffs, the cost of this API call has been dramatically reduced.

Test Plan: npm start, send and receive lots of transactions, change wallets, send and receive token txs

Reviewers: #bitcoin_abc, kieran709

Reviewed By: #bitcoin_abc, kieran709

Differential Revision: https://reviews.bitcoinabc.org/D11114