groups.json: western-palearctic in europe

Add 8 more island tiles: Madeira, Azores, Galapagos, New Caledonia, Cape Verde, Sao Tome & Principe, Seychelles, Mauritius; island-mode coverage maps

Add 5 small-island tiles: Iceland, Svalbard, Canary Islands (Europe), Reunion (Africa), Hawaii (Oceania)

Group regional catalog by continent (Europe/Asia/NA/SA/Africa/Oceania); add groups.json + group fields in metadata.json