[Cashtab] Build our own modal to stop using antd

Summary:
T2207

Build a custom modal for Cashtab. Can be maintained and modified easier than current antd modals.

Does not clear out all the antd modals but it's a good start.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15701