Added defaults for Playlist object.

core/src/main/sql/migrations/20151209054632-initial-schema-up.sql

@@ -52,7 +52,7 @@ CREATE TABLE playlists (
   name VARCHAR NOT NULL,
   mod_count INTEGER NOT NULL DEFAULT 0,
   media_file_count INTEGER NOT NULL DEFAULT 0,
-  copied_from_id INTEGER REFERENCES playlists(id)
+  copied_from_id INTEGER REFERENCES playlists(id) DEFAULT NULL
 );
 
 CREATE TABLE playlists_media_files (