Add Image MimeTypes

Author: mythz

src/ServiceStack.Text/HttpUtils.cs

@@ -842,6 +842,11 @@ public static class MimeTypes
         public const string MarkdownText = "text/markdown";
         public const string MsgPack = "application/x-msgpack";
         public const string NetSerializer = "application/x-netserializer";
+
+        public const string ImagePng = "image/png";
+        public const string ImageGif = "image/gif";
+        public const string ImageJpg = "image/jpeg";
+
         public const string Bson = "application/bson";
         public const string Binary = "application/octet-stream";
         public const string ServerSentEvents = "text/event-stream";