First cut of testing extensions

Adds async enumerable helper classes to EntityFramework.Testing

Adds a MockDebSet<T> to EntityFramework.Testing.Moq and the ability to
specify seed data and setup LINQ
Create nupkg's on build

Adding post build step to create NuGet packages on build
Also moving output to a central bin directory
Better descriptions for NuGet packages
Fix version of Moq->Core dependency