* Minor refactoring, constants moved to the CS class,
   and children of LevelActivity doesn't need to implement writeScore()
   method anymore. as of this revision each Activity has minimum
   required customization: only GridContainer.initLevelX()
   which X is a level number.
   (Note: This was one of refactorings that you feel better after,
          perhaps walk in the Pomegranate garden helped last night.)