* 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.
* Test that downloading the HTML page downloads the full size image
instead.
* Test that downloading a small or medium size image downloads the
full size instead.
* Test the above for both single illustrations and for manga galleries,
for new and old posts (i.e. uploaded before the Pixiv URL changes versus
after), and for different file extensions.
* Test trying to download ugoira zip files. These tests are expected to
fail because we don't support ugoira yet.
* Also add some more tests for fetching source data.
