[Cashtab] Improvements to app handling of new blocks

Summary:
Now that we have in-node chronik, we should only be triggering app updates that are block related on avalanche-finalized blocks.

1. The only app logic using blocks now is aliases. This should be gated by aliasSettings.aliasEnabled -- do this
2. Add notifications for found blocks. May remove this after halving but might be a nice touch. I like the info.

Test Plan:
npm test

desktop:

mobile:

This diff is deployed at https://cashtab-local-dev.netlify.app/ for live testing

Reminder ancient bitcoin dev law: if you are actively testing something that requires waiting for a block, please expect unusually long block times

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15889