Update skinning_loot_table entries for all skinnable mobs (and a few pickpocketing entries)

Tables like www.wowhead.com/npc=683 and www.wowhead.com/npc=688 were merged, treshold for percentage divergence was set to 1%.

1494 NPCs have been checked. (all PRE Mists, all skinnable)
589 loot table entries created
181 are pickpocketing entries
308 are skinning entries