Instead of having custom code check whether the artist name is already
in use, just enable autocomplete on the artist name field. This is an
easier and more robust way to indicate tag name conflicts.
* Rename Upload#download_for_upload to #get_file_for_upload.
* Fix #get_file_for_upload to raise error if no file or source url was given.
* Fix javascript upload validation to disallow submitting form if file is
not present and the source is not an url.
Bug: in the modqueue, if a user does a detailed rejection of one post,
then tries to do a detailed rejection of another post, the form will
still be filled in with the rejection message from the previous post.
Bug: if you open the tag edit dialog with shift+e, close it, then open
it again, it won't be vertically centered when it opens the second time.
Fix: hide the related tags section *before* opening the dialog, not after.
Hiding it afterwards shifts the layout, which uncenters the dialog.
Initialize the recent tags, frequent tags, translated tags, and artist
tags columns only once, when the related tags section is first shown.
The related tags section is shown automatically when the 'Edit' tab is
opened, or by default on the uploads page.
This fixes the /related_tags.js and /source.js calls being triggered
every time the tag edit dialog box or the 'Edit' tab was opened.
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.
ref: https://danbooru.donmai.us/forum_posts/151011
Bug: `Cookie.get("news-ticker") === key` always returned false because
the cookie was a string but the key was an integer.
Regressed in f72b32b27b after switching from `==` to `===`.
