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.

test/unit/post_test.rb

@@ -35,6 +35,7 @@ class PostTest < ActiveSupport::TestCase
         @post = @upload.post
         Favorite.add(post: @post, user: @user)
         create(:favorite_group, post_ids: [@post.id])
+        perform_enqueued_jobs # perform IqdbAddPostJob
       end
 
       should "delete the files" do
@@ -85,10 +86,9 @@ class PostTest < ActiveSupport::TestCase
       end
 
       should "remove the post from iqdb" do
-        mock_iqdb_service!
-        Post.iqdb_sqs_service.expects(:send_message).with("remove\n#{@post.id}")
-
         @post.expunge!
+        perform_enqueued_jobs
+        assert_performed_jobs(1, only: IqdbRemovePostJob)
       end
 
       context "that is status locked" do