Core/LFG: Minimum item level in Wotlk heroic dungeons

WotLK Heroics, beside Trial of the Champion, Pit of Saron, Halls of Reflection and The Forge of Souls unlock with an average item level of 160.
Also Trial of the Champion (normal) and The Forge of Souls (normal) unlock with an item level of 160.

http://www.wowwiki.com/Dungeon_Finder?oldid=2404648#Wrath_of_the_Lich_King_dungeons
Merge pull request #11095 from gerripeach/pull_request3

Core/LFG: Minimum item level in Wotlk heroic dungeons