keep rejected data rows in a separate list for debugging purposes

[hotzeplotz]

we currently simply drop any non-valid rows (i.e. missing date/time or lat/lon, or otherwise containing invalid data) whilst processing the GeoJSON data being loaded.

part of the filtering is already happening on data ingestion (pg_loader or POST to API), and in the longer term this is where all invalid content should be made available for review, including all relevant error messages that could help cleaning up the rows affected.

however, in the meanwhile - and whilst we load full datasets via XHR - it would be useful to make the list of rejected rows available within the frontend itself.

given that this is a somewhat transitory arrangement, we could probably just create a global list for this, and output to console a note about this and how to access the list.