Add methods to Source::URL for determining whether a URL is an image
URL, a page URL, or a profile URL.
Also add more source URL tests and fix various URL parsing bugs.
Refactor source strategies to remove the `canonical_url` method.
`canonical_url` returned the URL that should be used as the source of
the post after upload. Now we simply use `Source::URL#page_url` to
determine the source after upload. If the source is an image URL that is
convertible to a page URL, then the image URL is used as the source. If
the source is an image URL that is not convertible to a page URL, then
the page URL is used as the source.
This simplifies source strategies so that all they have to care about is
implementing the `Source::URL#page_url` and `Sources::Strategies#page_url`
methods, and the preferred source will be chosen for posts automatically.
Change how artist URLs are normalized in artist entries. Don't try to secretly
convert image URLs to profile URLs in artist entries. For example, if someone puts a
Pixiv image URL in an artist entry, don't secretly try to fetch the source and
convert it into a profile URL in the `normalized_url` field.
We did this because years ago, it was standard practice to put image URLs in artist
entries. Pixiv image URLs used to contain the artist's username, so we used to put
image URLs in artist entries for artist finding purposes. But Pixiv changed it so
that image URLs no longer contained the username, so we dealt with it by adding a
`normalized_url` column to artist_urls and secretly converting image URLs to profile
URLs in this field. But this is no longer necessary because now we don't normally put
image URLs in artist entries in the first place.
Now the `profile_url` method in `Source::URL` is used to normalize URLs in artist
entries. This lets us parse various profile URL formats and normalize them into a
single canonical form.
This also removes the `normalize_for_artist_finder` method from source strategies.
Instead the `profile_url` method is used for artist finding purposes. So the profile
URL returned by the source strategy needs to be the same as the URL in the artist
entry in order for artist finding to work.
Remove the `image_url` method from source strategies. This method would
return only the first image if a source had multiple images. The
`image_urls` method should be used instead. Tests were the main place
that still used `image_url` instead of `image_urls`.
Also make post replacements return an error if replacing with a source
that contains multiple images, instead of just blindly replacing the
post with the first image in the source.
* Move the source normalization logic out of the post model
and into individual sources' strategies.
* Rewrite normalization tests to be handled into each source's test,
and expand them significantly. Previously we were only testing
a very small subset of domains and variants.
* Fix up normalization for several sites.
* Normalize fav.me urls into normal deviantart urls.
