Move transcodes to be under CachePath

Move transcodes to be under CachePath instead of ProgramDataPath.

Since transcodes are ephemeral (they're cleaned up periodically and recreated if they don't exist), they're more like cache data than program data. Systems can (and oftentimes do) have the cache directory on a different disk, use a different type of file system, or have a different backup policy for the cache path because it contains ephemeral data.

MediaBrowser.Common/Configuration/EncodingConfigurationExtensions.cs

@@ -32,7 +32,7 @@ namespace MediaBrowser.Common.Configuration
             var transcodingTempPath = configurationManager.GetEncodingOptions().TranscodingTempPath;
             if (string.IsNullOrEmpty(transcodingTempPath))
             {
-                transcodingTempPath = Path.Combine(configurationManager.CommonApplicationPaths.ProgramDataPath, "transcodes");
+                transcodingTempPath = Path.Combine(configurationManager.CommonApplicationPaths.CachePath, "transcodes");
             }
 
             // Make sure the directory exists