Changes:
* Drop Users.id_to_name.
* Don't cache Users.name_to_id.
* Replace calls to name_to_id with find_by_name when possible.
* Don't autodefine creator_name in belongs_to_creator.
* Don't autodefine updater_name in belongs_to_updater.
* Instead manually define creator_name / updater_name only on models that need
to return these fields in the api.
id_to_name was cached to reduce the impact of N+1 query patterns in
certain places, especially in api responses that return creator_name /
updater_name fields. But it still meant we were doing N calls to
memcache. Using `includes` to prefetch users avoids this N+1 pattern.
name_to_id had no need be cached, it was never used in any performance-
sensitive contexts.
Avoiding caching also avoids the need to keep these caches consistent.
https://danbooru.donmai.us/forum_topics/9127?page=265#forum_post_153180:
> I'm not sure how to reproduce this, but sometimes on the upload page
> when I click the button to pop out the tag box, the screen scrolls up to
> the picture but the box doesn't pop out, and I have to scroll back down
> and click it again
https://danbooru.donmai.us/forum_topics/9127?page=266#forum_post_153183:
> Yes, this was brought up by Unbreakable on Discord a while back. It's
> due to the fact that the event handler that pops out the dialog box has
> not yet been bound by the time you click it. Since that clickable
> control has an empty anchor link of "#" which goes nowhere, it therefore
> redirects the user to the top of the page.
Refactor the /related_tags.js call so that when the "Related tags"
button is clicked, it only replaces the columns that actually changed,
not the entire related tags section.
This avoids rebuilding the Recent / Frequent / Translated Tags / Artist
columns every time the "Related tags" button is clicked.
Refactor tag_list_html, split_tag_list_html, and inline_tag_list_html to
take the `show_extra_links` and `current_query` options explicitly,
rather than implicitly relying on CurrentUser or taking `params[:tags]`
from the template.
* On posts, automatically trigger "Fetch source data" when clicking the
Edit tab, instead of triggering the artist finder button. This way we
find both the artist and the translated tags in one ajax call.
* Remove the "Artist" finder button next to the source field. This isn't
necessary given that "Fetch source data" finds the artist itself.
* Remove the /artists/finder.json API endpoint. This is no longer used
after removing the "Artist" finder button.
* On the /uploads/new page, instead of just showing a "This post has
probably already been uploaded" message, show the actual thumbnails of
posts having the same source as what the user is trying to upload.
* Move the iqdb results section up top, beside the related posts section.
Also makes it so that using the bookmarklet always triggers async upload
preprocessing. Before it was only triggered when the source passed a
dupe check, but that check was inaccurate (#3873).
to match the rest of the code base
For flash files I've used the file extension because the mime type is browser
specific and I've found at least 2 different variations for .swf:
1. `application/vnd.adobe.flash-movie`: wikipedia
2. `application/vnd.adobe.flash.movie`: mailcap, firefox
some other browser may not even know the .swf extension in the first place
