[eCash webdev libraries p3] Replace bitcoincashjs-lib with ecashjs-lib in Cashtab

Summary:
T2782

Depends on D12837

Now that ecashjs-lib is published on npm --- and is identical to the version currently used in Cashtab, bitcoincashjs-lib, replace bitcoincashjs-lib with ecashjs-lib

Going forward, we will be able to make improvements to ecashjs-lib and test them in Cashtab.

Test Plan:
npm start
Send an XEC tx
Send an eToken tx
grep -r '@psf/bitcoincashjs-lib' src/ yields no results

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12838