Snap Trap placeholder anims

Set up animation data for Snap Trap so it can be easily replaced with a proper animation later.

include/constants/battle_anim.h

@@ -569,6 +569,7 @@
 #define TRAP_ANIM_SAND_TOMB 4
 #define TRAP_ANIM_MAGMA_STORM 5
 #define TRAP_ANIM_INFESTATION 6
+#define TRAP_ANIM_SNAP_TRAP 7
 
 // Weather defines for battle animation scripts.
 #define ANIM_WEATHER_NONE 0