iqdb: update API client to use new version of IQDB.

Replace the old IQDB API client with a new client for the new forked
version of IQDB at https://github.com/danbooru/iqdb.

Changes:

* The /iqdb_queries endpoint now returns `hash` and `signature` fields.
  The `signature` is the full decoded Haar signature, while the `hash`
  is a encoded version of the signature.
* The /iqdb_queries endpoint no longer returns `width` and `height`
  fields in the response (these were always 128x128).
* We no longer need the IQDBs frontend server, now we talk to the IQDB
  instance directly.
* We no longer send add/remove image commands to IQDB through AWS SQS,
  now we send them to IQDB directly. They are sent in a delayed job so
  that if IQDB is down, uploading images is still possible, the add
  image commands will just get queued up.
* Fix a bug where regenerating an image's thumbnails didn't regenerate
  IQDB, because IQDB silently ignored add image commands when the image
  already existed in the database.

lib/tasks/iqdb.rake

@@ -2,8 +2,7 @@ namespace :iqdb do
   task reindex_posts: :environment do
     STDIN.each_line do |post_id|
       puts post_id
-      post.remove_iqdb_async
-      post.update_iqdb_async
+      post.update_iqdb
     end
   end
 end