Add GetAbsoluteUrlString

Common.csproj

@@ -146,6 +146,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="DateTimeExtensions.cs" />
+    <Compile Include="Internet\UrlHelper.cs" />
     <Compile Include="IO\ProcessAsync.cs" />
     <Compile Include="Properties\Resources.Designer.cs">
       <AutoGen>True</AutoGen>

Internet/UrlHelper.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Common.Internet
+{
+    public static class UrlHelper
+    {
+        public static string GetAbsoluteUrlString(string baseUrl, string url)
+        {
+            var uri = new Uri(url, UriKind.RelativeOrAbsolute);
+            if (!uri.IsAbsoluteUri)
+                uri = new Uri(new Uri(baseUrl), uri);
+            return uri.ToString();
+        }
+    }
+}