Refactor source normalization

* 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.

app/logical/sources/strategies/tumblr.rb

@@ -5,6 +5,8 @@
 # https://emlan.tumblr.com/post/189469423572/kuro-attempts-to-buy-a-racy-book-at-comiket-but
 # https://66.media.tumblr.com/168dabd09d5ad69eb5fedcf94c45c31a/3dbfaec9b9e0c2e3-72/s640x960/bf33a1324f3f36d2dc64f011bfeab4867da62bc8.png
 # https://66.media.tumblr.com/5a2c3fe25c977e2281392752ab971c90/3dbfaec9b9e0c2e3-92/s500x750/4f92bbaaf95c0b4e7970e62b1d2e1415859dd659.png
+#
+# https://superboin.tumblr.com/post/141169066579/photoset_iframe/superboin/tumblr_o45miiAOts1u6rxu8/500/false
 
 module Sources::Strategies
   class Tumblr < Base
@@ -131,6 +133,12 @@ module Sources::Strategies
       super(tag)
     end
 
+    def normalize_for_source
+      return unless blog_name.present? && post_id.present?
+
+      "https://#{blog_name}.tumblr.com/post/#{post_id}"
+    end
+
     def dtext_artist_commentary_desc
       DText.from_html(artist_commentary_desc).strip
     end