Revert "Revert "[Cashtab] Convert wallet context to ts""

Summary:
This reverts commit b88a433009eaca5a4fcb685f7a611665f115881b.

Identified and resolved the bug that caused this to fail builds in prod. Was an issue with not properly initWasm()

See updated file cashtab/src/index.tsx and the much lighter lint-related changes that are applied here vs in the original diff.

Test Plan:
npm test
npm start and app loads
npm run build and app builds

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D17311