* 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.
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.
