[Cashtab] Create new wallets with ecash address

Summary:
T2836

Generate new wallets with cashAddress in ecash: format. Make sure this doesn't break anything.

Test Plan:
npm start
Create a new wallet
Activate it
Receive an XEC tx
Send an XEC tx
Receive an eToken tx
Send an eToken tx

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12761