By default, use area-based alerts.

The body-based alert only works if the body ID matches the MapIt ID.
This fixes #959. Further work needs to be done to enable proper
body-based alerts that work properly in all circumstances.

Consequently, factor out fixed body IDs from many tests.
Also fix a couple of tests not overriding geocoder correctly.
Add a script to always test on a clean db/config.

Fixes #786.