Implemented a new Submission client using HttpClient and general cleanup

Author: niemyjski

src/Exceptionless.Portable/Extensions/ClientExtensions.cs

@@ -1,18 +1,11 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-using Exceptionless.Threading.Tasks;
 
 namespace Exceptionless.Extensions {
     internal static class EnumerableExtensions {
         public static void AddRange<T>(this ICollection<T> list, IEnumerable<T> range) {
             foreach (var r in range)
                 list.Add(r);
         }
-
-        public static Task ForEachAsync<T>(this IEnumerable<T> source, Func<T, Task> body) {
-            return Task.Factory.WhenAll(source.Select(body));
-        }
     }
 }