Changed default database location from in-memory to a relative file.

src/main/java/musicplayer/ConfigManager.java

@@ -60,7 +60,13 @@ public final class ConfigManager {
             }
         } catch (IOException ignored) {
         }
-        return "jdbc:hsqldb:mem:."; // If not set use an in-memory database for now.
+        librarySettings.setProperty(databaseKey, "musicDB");
+        try(FileWriter fileWriter = new FileWriter(settingsFilename)){
+            librarySettings.store(fileWriter, "");
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return "jdbc:hsqldb:file:" + new File("musicDB").getAbsolutePath() + ";shutdown=true"; //Use relative file by default
     }
 
     /**