[electrum] Install custom eCash firmware on Trezor
Summary:
This custom firmware makes it possible to sign stakes using a Trezor (T, Safe 3 or 5).
Depends on D17798.
Test Plan: Tested on all Trezor devices.
Reviewers: #bitcoin_abc, PiRK, Mengerian
Reviewed By: #bitcoin_abc, PiRK, Mengerian
Subscribers: Mengerian, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D17799