Added a generic interface for retrieving images. Where multiple images exist, it'll retrieve the least seen. If there are sufficient images to work with, it'll randomly pick from a subset of the least seen to make it less predictable what's going to show up.

KfChatDotNetBot/Program.cs

@@ -17,6 +17,8 @@ namespace KfChatDotNetBot
             await BuiltIn.SyncSettingsWithDb();
             logger.Info("Migrating settings from config.json (if needed)");
             await BuiltIn.MigrateJsonSettingsToDb();
+            logger.Info("Migrating images over to the new system");
+            await BuiltIn.MigrateImages();
             logger.Info("Handing over to bot now");
             Console.OutputEncoding = Encoding.UTF8;
             new ChatBot();