Add a Suggested tags list to the Related Tags box. The suggested tags
are just the AI tags for the post.
Suggested tags are currently hidden in CSS for beta testing. Use custom
CSS to unhide them.
* Add "general" rating.
* Rename "safe" rating to "sensitive".
* Change safe mode to include both rating:s and rating:g.
* Treat rating:safe as a synonym for rating:sensitive.
* Link "howto:rate" in the post edit form.
Refactor ratings to not be hardcoded in various places. Make it so
all ratings are defined in Post::RATINGS.
Also make it so that you can search multiple ratings at once with `rating:q,e`.
Refactor source strategies to remove the `canonical_url` method.
`canonical_url` returned the URL that should be used as the source of
the post after upload. Now we simply use `Source::URL#page_url` to
determine the source after upload. If the source is an image URL that is
convertible to a page URL, then the image URL is used as the source. If
the source is an image URL that is not convertible to a page URL, then
the page URL is used as the source.
This simplifies source strategies so that all they have to care about is
implementing the `Source::URL#page_url` and `Sources::Strategies#page_url`
methods, and the preferred source will be chosen for posts automatically.
Fixes an issue where if you were uploading a multi-image source, and you
clicked on a thumbnail that was still processing, then the page wouldn't
refresh when the processing was complete.
