change game over display

game over screen is now displayed in HighscoreActivity,
where it asks for a name to save score with.

loading highscore from app cache and storing it back is
now handled in HighscoreActivity instead of SplashActivity.
refine new game over display and add name field in highscore

 * New images for buttons and headings
 * layout changes, added "replay" button
add name field to highscore display
remove redundant code and fix few bugs