Figure out reconnections to Electrum server

[tnull]

In #486, we added initial support for sourcing chain data from an Electrum server based on rust-electrum-client.

Unfortunately, the latter doesn't handle connection failures at all really. So a dropped connection would likely just result in a unusable Client object. As this this needs to be handled/fixed upstream I opened bitcoindevkit/rust-electrum-client#165. But, if it's no fixed upstream, we have to come up with some resolution here.

Marking as 'blocked on upstream' for now.