refs #2 Level two (Daisy)
 * See GridContainerLevel2Test.java for new add tested logics in the
   game.
 * Level 2 works similar to Level 1 but using slightly different
   implementation, for example base class LevelActivity introduced to
   factor some common functionalities for further levels.
refs #3 Game score and one-step-back feature
 * Game score is visiable in first page as off this revision.
 * one-step-back feature is done as off this revision.
   plus minor improvements for user interfaces.