minor fixes to imdb's outputs

This fixes #194
Additionally,
1) the plugin was supposed to insert (but was not doing so) replace the last comma with an "and" if there was no director listed, eg "...starring Ashley Benson, Shay Mitchell, Lucy Hale[ and ]Troian Bellisario."
2) "M" has been added to the list of ratings that needs to be written as "an M rated title..."
3) plugin no longer displays N/A if there is no plot synopsis provided by api
4) plugin displays "title" in place of N/A if the type (eg movie, episode, etc) is not provided by the api