Add cursed apple: a status-effect apple that inverts controls

Eating a cursed apple inverts the snake's steering for
CURSE_DURATION_TICKS ticks, shown on the top screen while active. The
sprite is a recolored copy of the rotten-apple tile since all existing
sprite tiles are already in use.

include/consts.h

@@ -5,6 +5,7 @@
 const int START_LENGTH = 4;
 const int START_LENGTH_HARD =2;
 const int APPLE_SCORE = 10;
+const int CURSE_DURATION_TICKS = 40;
 
 //Screen size
 const int X_MAX = 31;