Fix EPS and build it into Electrum

[ecdsa]

Electrum Personal Server is middleware that allows use Electrum with a bitcoind instance. https://github.com/chris-belcher/electrum-personal-server

The current version EPS cannot be used with Lightning wallets, because it only indexes addresses derived from the wallet xpub. This could be fixed, by passing bitcoin addresses to bitcoind. Unfortunately, the EPS maintainer is no longer active, so this has never been done.

I think we should:

• fix EPS so that it works with arbitrary addresses
• build EPS into Electrum, in order to remove user friction and ensure it remains maintained.

Anyone interested to work on that project, please let us know here.

[Talkless]

It seems that this is now very dire need with legacy wallet being removed from Bitcoin Core: https://github.com/chris-belcher/electrum-personal-server/issues/309