Prepare TraktRateDialogFragment for movie rating.

- Clean up TraktAction enum usage.
Add movie seen/unseen support to TraktTask.

- Also refactor a little.
- Dropped unused SEEN_EPISODE TraktAction.
When connected to trakt, support watched state on movies.
Display localized message when flagging movie seen/unseen on trakt.
Add rating support for movies.
Ratings cache ignores old entries, caches show ratings, too.

- Fixes https://github.com/UweTrottmann/SeriesGuide/issues/345.
Merge branch 'movie-watch-rate' into beta