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.
Derive the artist name / profile url / page url from the source URLs when
the API response is unavailable because the Tumblr post was deleted.
This fixes the artist finder to work on bad_tumblr_id posts.
If the yande.re or konachan.com post has a source from a supported site,
for example Pixiv or Twitter, then delegate the artist and commentary
lookup to that substrategy.
Only do this for sources from recognized sites, not the null strategy.
Move Post#humanized_essential_tag_string to TagSetPresenter#humanized_essential_tag_string.
This allows humanized_essential_tag_string to reuse the same set of tags
already fetched by the tag set presenter for the sidebar.
This avoids fetching the tag categories from memcache again (via
Post#typed_tags) when we're already fetched the tags once before.
This also means it's no longer necessary to cache humanized_essential_tag_string
itself in memcache, since it can be generated as quickly as the sidebar taglist.
Allow searching the URL field by regex or by wildcard.
If the query looks like `/twitter/` do a regex search, otherwise if it
looks like `http://www.twitter.com/*` do a wildcard search, otherwise if
it looks like an url do an artist finder search, lastly if it looks like
`twitter` do a `*twitter*` search.
* Move the limit:<n> / order:random metatag parsing from the controller
to the post set.
* Introduce `Tag.has_metatag?` and use it to parse these metatags
instead of using a regex (#2894).
Fixes the banned IP check not being applied when sending the HEAD
request for is_cloudflare?.
Also fixes the `#size` method not using the uncached url (which meant
the bookmarklet could report the wrong filesize on artstation uploads).
