Add Dream World item artwork.

Unlike the pokemon artwork, the item artwork was unfortunately not
available in a vector format.

Some items do not have dream world artwork: all key items, mail, TMs and
HMs, Wonder Launcher items, Data Cards (from HG/SS), and the following
items:

 - Mulches
 - RageCandyBar
 - Cherish Ball and Dream Ball
 - Odd Keystone
 - Griseous, Adamant, and Lustrous Orbs
 - Burn, Chill, Douse, and Shock Drives