Sprite Library updates

Added Sprites (those that were available, at least) for the Kalos
Pokémon, and filled the empty entries with placeholder sprites.

Updated header to reflect additions.

Added Egg Sprite (index 722).

Added Unown sprites B - Z. Some bugs regarding ! and ? to be fixed in
future.

Added alternate sprites for Pokémon with formes (not including those
related to sexual dimorphism) for species 0 (Missingno) through to 586
(Sawsbuck).