Change visibility of Song(ParseObject) constructor.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>
Add default implementation of equals and hashCode for models.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>
Add a wrapper model class for a party.

Signed-off-by: Aron Cedercrantz <aron@cedercrantz.se>