[e.cash] Add functions to fetch exchanges and score and sort them

Summary:
Function to fetch scorecard.cash exchange list
Function to score the responses based on some added scoring criteria
Function to make sure the sorted list is divisible by three
Test for all the functions

Test Plan:
npm run test
see if all test pass

Reviewers: #bitcoin_abc, bytesofman, Fabien

Reviewed By: #bitcoin_abc, bytesofman, Fabien

Subscribers: Fabien, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14056