Xamarin.iOS and Xamarin.Android support for JabbR.Client

I've added a .sln file to support JabbR.Client on Xamarin.iOS and Xamarin.Android

The one 'gotcha' right now is I had to add binaries of Microsoft.AspNet.SignalR.Client.Android.dll into the lib folder since the currently stable version of NuGet doesn't support monoandroid or monotouch (it does in the release candidate). An alternative would be to start packaging releases of the SignalR client for the Xamarin Component store.  I've also got the iOS and Android binaries for Newtonsoft.Json.Net.dll similar to how the SignalR does this right now.