[Cashtab] Pull to refresh feature

Summary:
Mobile users expect a "pull to refresh" option. In this case, we should just refresh the URL of the app, which will refresh the current component. This could correct app state after missed websocket msgs or other loading errors.

Implement as a custom component. We may need to tweak some variables depending on user feedback (e.g. perhaps it is too sensitive and triggers inadvertent refreshes).

Test Plan: npm test, npm start and test it out in mobile, you can do it, but you can also scroll up on tx history without doing it

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D19197