[connectors] Import and use GeoJSON-to-Postgres script across other connector scripts

[rudokemper]

Feature Request

#81 introduced a GeoJSON-to-postgres script which can be imported and used by other connector scripts that end up writing GeoJSON to the database.

#87 introduced a save_export_file function to save incoming data to disk.

Let's refactor the following scripts to use this code as a module import:

• arcgis_feature_layer
• comapeo_observations
• globalforestwatch
• locusmap

One of the reasons for doing so is stated in #81:

[Doing so] would minimize redundant DB write logic and, if we ever adopt PostGIS, allows us to update the implementation in one place.

Additionally, we can start to save upstream data (e.g. from CoMapeo, Locus Map) to disk as GeoJSON file, which most users eventually end up wanting anyway.