Plato 0.9.14

The metadata format has changed, manual intervention is required.

Within each library's path, run the attached python script:

mv .metadata.json .metadata-old.json
./migrate-hex_keys.py < .metadata-old.json > .metadata.json

Notable changes:

• Add a menu item to empty the trash.
• Move the database's clean up routine to Library::import.
• Make a few adjustments to the hooks API.