[e.cash] Add Edge Wallet

Summary:
It now supports eCash

Logo from https://github.com/EdgeApp/edge-brand-guide

Test Plan: Run it locally, read description to make sure it sounds good

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18277