Added some configuration validation stuff but then realised probablt wont need this for a while

src/Ocelot.Library/Infrastructure/Configuration/ConfigurationValidationResult.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Ocelot.Library.Infrastructure.Configuration
+{
+    public class ConfigurationValidationResult
+    {
+    }
+}

src/Ocelot.Library/Infrastructure/Configuration/ConfigurationValidator.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Ocelot.Library.Infrastructure.Responses;
+
+namespace Ocelot.Library.Infrastructure.Configuration
+{
+    public class ConfigurationValidator : IConfigurationValidator
+    {
+        public Response<ConfigurationValidationResult> IsValid(Configuration configuration)
+        {
+            var duplicateUpstreamTemplates = configuration.ReRoutes
+                .Select(r => r.DownstreamTemplate)
+                .GroupBy(r => r)
+                .Where(r => r.Count() > 1)
+                .Select(r => r.Key)
+                .ToList();
+
+            if (duplicateUpstreamTemplates.Count <= 0)
+            {
+                return new OkResponse<ConfigurationValidationResult>(new ConfigurationValidationResult());
+            }
+                
+            var errors = new List<Error>();
+
+            foreach (var duplicateUpstreamTemplate in duplicateUpstreamTemplates)
+            {
+                var error = new DownstreamTemplateAlreadyUsedError(string.Format("Duplicate DownstreamTemplate: {0}", 
+                    duplicateUpstreamTemplate));
+                errors.Add(error);
+            }
+
+            return new ErrorResponse<ConfigurationValidationResult>(errors);
+        }
+    }
+}

src/Ocelot.Library/Infrastructure/Configuration/DownstreamTemplateAlreadyUsedError.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Ocelot.Library.Infrastructure.Responses;
+
+namespace Ocelot.Library.Infrastructure.Configuration
+{
+    public class DownstreamTemplateAlreadyUsedError : Error
+    {
+        public DownstreamTemplateAlreadyUsedError(string message) : base(message)
+        {
+        }
+    }
+}

src/Ocelot.Library/Infrastructure/Configuration/IConfigurationValidator.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Ocelot.Library.Infrastructure.Responses;
+
+namespace Ocelot.Library.Infrastructure.Configuration
+{
+    public interface IConfigurationValidator
+    {
+        Response<ConfigurationValidationResult> IsValid(Configuration configuration);
+    }
+}