Electrum: add support for socks5 proxies

[sstone]

We use the same socks5 proxy that is optionally enabled in the configuration and is typically used to connect to LN nodes running as TOR hidden services.

This will allow eclair:

• to connect to .onion Electrum servers running behind TOR
• to connect to regular Electrum servers through TOR

[codecov-io]

Codecov Report

Merging #1315 into master will increase coverage by 0.15%.
The diff coverage is 75%.

@@            Coverage Diff            @@
##           master   #1315      +/-   ##
=========================================
+ Coverage   77.45%   77.6%   +0.15%     
=========================================
  Files         144     144              
  Lines       10130   10132       +2     
  Branches      414     392      -22     
=========================================
+ Hits         7846    7863      +17     
+ Misses       2284    2269      -15

Impacted Files	Coverage Δ
...ir-core/src/main/scala/fr/acinq/eclair/Setup.scala	73.29% <0%> (ø)	⬆️
...clair/blockchain/electrum/ElectrumClientPool.scala	82.79% <100%> (+4.3%)	⬆️
...nq/eclair/blockchain/electrum/ElectrumClient.scala	73.83% <100%> (+0.18%)	⬆️
...in/scala/fr/acinq/eclair/channel/Commitments.scala	90.68% <0%> (+0.35%)	⬆️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	83.68% <0%> (+0.45%)	⬆️
...src/main/scala/fr/acinq/eclair/router/Router.scala	92.56% <0%> (+0.67%)	⬆️
...q/eclair/blockchain/electrum/ElectrumWatcher.scala	55.2% <0%> (+0.8%)	⬆️

[t-bast]

LGTM, how can we test that? With a manual test on a machine with Tor?

[sstone]

Yes, with a manual test using Tor's default proxy (just setting eclair.socks5.enabled to true should be enough)