Fixes and 64bit compatibility for SQLite

Removed compiler warnings (duplicated usings, wrong reference paths)
Replaced System.Data.SQLite.dll with NuGet Package -> 64bit compatibility
Replaced obsoleted ProhibitDtd
Replaced obsoleted SetSubType
Fixed Addonpack.csproj duplicated references (RGBVector, MonoFlop, Swizzle4d)

Hope it's not to much for one pull request :)