[Cashtab] Update hardcoded references to the old cashtabapp.com domain

Summary:

• Updated hardcoded references to the old cashtabapp.com domain
• References in coverage reports and mock params as part of the test suite have been left unchanged
• Updated Configure.js snapshot

Test Plan:

• npm start
• verify no externally facing links displaying the old cashtabapp.com domain

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10393