[Cashtab] Add props validation and clean up resulting lint errors

Summary:
T1723

React supports basic type checking for development which is useful in debugging or catching errors. Cashtab did not have this previously. It always "should" have been there, but might as well start now.

Removed any unused props from the check. Standardized format of export default for any component that is the only component in a file.

Test Plan:
npm start
Click through all screens with dev console open and verify no errors.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10001