Move the call to normalize_for_artist_finder! from the artist
controller into Artist#find_all_by_url. This makes testing easier.
It also makes it so that URLs are normalized when using the search
form on the artist listing page.
Refactors things such that Sources::Site has a normalize_for_artist_finder!
method that delegates to the strategy for the appropriate site. This way
any site that needs to normalize URLs for the artist finder can do so.
There are two kinds of thumbnails that need to be rewritten. First case:
new /img-master/ URLs need to be rewritten to /img-original/ URLs like this:
http://i2.pixiv.net/c/600x600/img-master/img/2014/10/04/03/59/52/46337015_p0_master1200.jpg
=> http://i2.pixiv.net/img-original/img/2014/10/04/03/59/52/46337015_p0.png
This is what `rewrite_new_medium_images` does. In order to do this, it
has to use the Pixiv API to get the correct file extension.
Second case: Old small/medium size URLs need to be rewritten to full
size URLs like this:
http://i2.pixiv.net/img18/img/evazion/14901720_m.png
=> http://i2.pixiv.net/img18/img/evazion/14901720.png
But when the medium size URL is actually for a manga image, it needs to be
rewritten to the big manga URL instead:
http://i2.pixiv.net/img04/img/syounen_no_uta/46170939_m.jpg
=> http://i2.pixiv.net/img04/img/syounen_no_uta/46170939_big_p0.jpg
But we can't tell whether it's a manga image from the URL, so we have to
use the manga page count from either the HTML page or the API to
determine whether it's part of a manga gallery.
So in order to make this work, `rewrite_old_small_and_medium_images`
takes an `is_manga` flag. `Sources::Strategies::Pixiv#get` gets the
page count from the HTML and passes the `is_manga` flag on down through
the call chain until `rewrite_old_small_and_medium_images` gets it.
When `rewrite_old_small_and_medium_images` is called from
`Downloads::Strategies::Pixiv#rewrite_thumbnails`, the `is_manga` flag
isn't passed in because we didn't scrape the HTML. This causes
`rewrite_old_small_and_medium_images` to look it up in the API instead.
