Added new service API call to only get the directories from a certain storage group.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
Added new service API calls to rename or delete a certain file.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
Updated the DeleteFile and RenameFile service API methods to use storage groups. Added more checks to the RenameFile method.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>