Added major islands of Sweden (Gotland, Öland and Holmöarna).

Islands close to mainland are already included due to border feathering, such as Orust.
Added major islands of Sweden (Gotland, Öland and Holmöarna) to the complete countries geo.
Merge pull request #15 from carlcalderon/master

Added major islands of Sweden (Gotland, Öland and Holmöarna).