* Add geojson and mapbox-styles files for overlays
* Update stats config to include overlays property

When the same overlay is loaded from the repo
and as a global overlay the repo one is preferred.

These files are also added via the cached-data mechanism
in cadence (commit 1d0799a5ec).
This change adds them at source, so this cached-data step
can be reduced.

An trailing newline is added to one of the geojson files
compared to the version in cadence's cached-data dir. This
is to ensure the fake-repo-setup script does not error
in an attempt to commit when there are no changes. This
avoids the need for a cadence change to proceed this one.