Update Newtonsoft.Json from 4.5.11 to 6.0.6

Signed-off-by: Ryan Hatfield <tophathacker@gmail.com>
Moved files into PodioNet.PCL where allowed, so they can be used with Xamarin mobile projects.

Also enabled package restore and removed the packages folder from source control.

Signed-off-by: Ryan Hatfield <tophathacker@gmail.com>