sources: add image_url?, page_url?, and profile_url? methods.

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.

app/logical/source/url/fandom.rb

@@ -44,6 +44,10 @@ class Source::URL::Fandom < Source::URL
     end
   end
 
+  def image_url?
+    full_image_url.present?
+  end
+
   def wiki
     WIKI_DB_NAMES.fetch(wiki_db_name, wiki_db_name)
   end