Incremental import

[scy]

Currently, importing new MEPs into an existing database is not really possibly. Neither is “remove all MEPs from the database that do not appear in this most recent import”. Instead, all imports assume an empty database.

The possibility to do this should be implemented, because throwing away the live data during a running campaign isn’t ideal, to put it mildly.

Care must be taken not to break existing relationships or assumptions.

[jbethune]

Looks like we would need to check if an entry already exists around here. I think that deleting MEPs/destinations from the database should not be part of the import functionality but a different feature in order to keeps simple and to distinguish constructive and destructive actions.