Should shapes be exploded into individual Polygons?

[irm-codebase]

Is your feature request related to a problem? Please describe.
I've noticed that often we want to eliminate certain bits from shapefiles.
These can be islands, some oddball region, etc.

This is near-impossible to filter if the shapefile itself is a multipolygon.

Describe the solution you'd like
So, the proposal is to:

1. Ensure each element in the final shape file is a simple corrected Polygon, even when requesting NUTS0 or country aggregation.
2. Add some specific identifier to these exploded regions.
3. Add an option to remove specific IDs in the configuration. If found, it is removed.

Implementing this should be straight forward.