Upgrade to xUnit 2

Fixes #628 

 - [x] migrated tests over to new infrastructure
 - [x] VS runner packages included for VS2013+
 - [x] console runner included for CI scripts
 - [x] Is Appveyor Happy?
 - [x] cleanup all the things
This is just so the files aren't committed. NuGet should skip installation if the folder exists on disk, and the caching should mean it doesn't hit the network after the first installation. :cool:?