Don't comment out example configuration

Breaks the mySociety internal deployment tooling.
Merge branch 'hotfix/0.19.0.12'
Merge branch 'release/0.20'

Conflicts:
  config/general.yml-example
Try to avoid n+1 queries, and multiple admin authority queries.

Attempting to make the import faster when there are lots of public authorities in the database already
Merge branch 'hotfix/0.20.0.1' into wdtk