* Tighten up illust id parsing to avoid misparsing ids from
non-illust urls (sketch urls and novel urls).
* Move id parsing tests from post_test.rb to sources/pixiv_test.rb.
* Drop support for touch.pixiv.net urls. These urls are no longer used
by Pixiv and aren't present as the source of any posts on Danbooru.
Bug: Uploading bad pixiv id images failed because the pixiv strategy
raised a BadIDError exception when the upload service checked for the
ugoira frame data.
* Rename `unique_id` to `tag_name`.
* Add `other_names` and `profile_urls` methods that sources can override
to provide extra names or urls when creating new artist entries.
* Normalize spaces to underscores when saving other names. Preserve case
since case can be significant.
* Fix WikiPage#other_names_include to search case-insensitively (note:
this prevents using the index).
* Fix sources to return the raw tags in `#tags` and the normalized tags
in `#normalized_tags`. The normalized tags are the tags that will be
matched against other names.
Fix sources choosing the wrong strategy when the referer belongs to a
different site (for example, when uploading a twitter post with a pixiv
referer).
* Fix `match?` to only consider the main url, not the referer.
* Change `match?` to match against a list of domains given by the `domains` method.
* Change `match?` to an instance method.
* 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.
* Only suggest the Danbooru tag with the same name if there is no
matching wiki other name. Example: if we have the Pixiv tag `Fate` and
the Danbooru tag `fate_(series)` with other name `fate`, suggest that,
not the Danbooru tag `fate`.
* Don't suggest tags that are empty or whose wiki is deleted.
* Only split tags on "/" if there are no other matches, and only for Pixiv.
* For Pixiv, only include traditional media tags in tag list, not digital media (Photoshop, SAI).
* Add some tests.
* Make illust_id_from_url a public class method instead of a protected
instance method so that Post#parse_pixiv_id can use it.
* Also make illust_id_from_url swallow the exception that
illust_id_from_url! throws so that parse_pixiv_id can use it.
