Function to modify the labels on a given thread by id.
Arguments
- id
- thread id to access 
- add_labels
- labels to add to the specified thread 
- remove_labels
- labels to remove from the specified thread 
- user_id
- gmail user_id to access, special value of 'me' indicates the authenticated user. 
See also
Other thread: 
gm_delete_thread(),
gm_threads(),
gm_thread(),
gm_trash_thread(),
gm_untrash_thread()