Feature variables v2.01 with bugfix (#164)

* Changed Variables.cs to full IDictionary
with ConcurrentDictionary<string, object> backing

* Bugfix for long running flows

src/core/Elsa.Abstractions/Models/Variables.cs

@@ -108,6 +108,12 @@ namespace Elsa.Models
         {
             object value;
             objects.TryGetValue(name, out value);
+
+            if(value != null && ((value.GetType() == typeof(JValue) || value.GetType() == typeof(JToken)) && value.GetType() != typeof(T)))
+            {
+                value = ((JToken)value).ToObject<T>();
+            }
+            
             return value == null ? default : (T)value;
         }