Upgrade Electrum to 3.1.1+

Electrum is under very rapid development. We want to make sure that our users have the latest version. Only two packages need to be updated: electrum and python3-electrum. Specifically, this update means that we can use the improved configuration in Bug #15483 (closed) among many other improvements listed in https://github.com/spesmilo/electrum/blob/master/RELEASE-NOTES .

Related issues

Blocks #15483 (closed)

Original created by @mjenglish on 15484 (Redmine)

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