Update all gatherable loot templates for creatures

-- Treshold set to 1% (eg. tables from www.wowhead.com/npc=683 and
www.wowhead.com/npc=688 have been merged.)
-- Created 510 Skinning entries with 1807 Items.
-- Created 70 Herbalism entries with 923 Items.
-- Created 40 Mining entries with 143 Items.
-- Created 20 Engineering entries with 136 Items.
-- Created 3242 Pickpocketing entries with 17064 Items.
-- Updated total of 46625 creature_template entries.