Added 20 sets to [DGC] Collection

Previews & DDL:

	[DGC] 2008.05 No.581 Nana Nanaumi 七海なな
	[DGC] 2008.05 No.582 Reimi Tachibana 橘麗美
	[DGC] 2008.05 No.583 Mana Aikawa 逢川麻奈
	[DGC] 2008.05 No.584 Hatsumi Yoshida 吉田初美
	[DGC] 2008.05 No.585 Rio Yagisawa 八木沢莉央
	[DGC] 2008.05 No.586 Yumi Ishikawa 石川優実
	[DGC] 2008.06 No.587 Nonami Takizawa 滝沢乃南
	[DGC] 2008.06 No.588 Yuuki Fukasawa 深澤ゆうき
	[DGC] 2008.06 No.589 Natsumi Kamata 鎌田奈津美
	[DGC] 2008.06 No.590 Nanako Kodama 児玉菜々子
	[DGC] 2008.06 No.591 Maki Aizawa 相沢真紀
	[DGC] 2008.06 No.592 Yuma Asami 麻美ゆま
	[DGC] 2008.06 No.593 Aino Kishi 希志あいの
	[DGC] 2008.06 No.594 Mikuro Shimizu 志水みくろ
	[DGC] 2008.06 No.595 Wakana わかな
	[DGC] 2008.06 No.596 Akari Saito 齋藤朱莉
	[DGC] 2008.06 No.597 Nao Inamoto 稲本奈緒
	[DGC] 2008.06 No.598 Miyuki Koizumi 小泉みゆき
	[DGC] 2008.07 No.599 Aya Kiguchi 木口亜矢
	[DGC] 2008.07 No.600 Nao Nagasawa 長澤奈央