[Cashtab] Convert some common components to ts

Summary:
Part of ongoing effort to convert Cashtab to ts

Convert some small Common components to ts

Decision to include these particular components is arbitrary. Felt like doing just one was too small a diff. Adding any more was too much for one diff.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17401