Complete BridgeDB upgrades phase 1

This project ticket replaces the milestone "BridgeDB Upgrades Phase 1" and contains all tickets as child tickets that were assigned to that milestone.

(Milestones are the wrong concept here. It's not a milestone of the sort "let's see which tasks we need to complete before releasing a new BridgeDB version." It's a project with a given scope, and we want to remember which tasks belong to this project.)

Speaking of, which sponsor wants to see this project done, or is it a sponsor Z thing? Maybe we should assign this project ticket to a sponsor milestone, or otherwise we may never finish it.