Shared/Build: Restore disabled warnings on Visual Studio

Restore 2 disabled warnings, 1 already disabled in CMake with the WITH_WARNINGS flag set to False and the other disabled by default as stated in VS documentation http://msdn.microsoft.com/en-us/library/aa984150.aspx
DB/SAI: The Battle of Valhalas Quest Chain

Fixes #8377
Consists of:
1) Battle at Valhalas: Fallen Heroes (13214)
2) Battle at Valhalas: Khit'rix the Dark Master (13215)
3) Battle at Valhalas: The Return of Sigrid Iceborn (13216)
4) Battle at Valhalas: Carnage! (13217)
5) Battle at Valhalas: Thane Deathblow (13218)
6) Battle at Valhalas: Final Challenge (13219)
Merge pull request #10827 from jackpoz/restore_warnings

Shared/Build: Restore disabled warnings on Visual Studio
Merge branch 'master' of github.com:TrinityCore/TrinityCore