Support version 8 exports in load_export

https://redmine.teklia.com/issues/7320

In #1723 (closed), we bumped the export version to 9 and deleted the entity_link and entity_role tables. We could still support importing exports of the previous version, as we only have to ignore those tables completely.

Please replace the EXPORT_VERSION constant in load_export with EXPORT_VERSION_MIN and _MAX, and check that the version is between those two values (inclusive), so that the command supports export versions 8 and 9.

The tables check should check that the database's tables are a superset of TABLE_NAMES, not that they are exactly TABLE_NAMES, so that any tables we don't know and don't care about are ignored and the export can proceed.