twitter: replace twitter gem with our own API client.

The twitter gem had several problems:

* It's been unmaintained for over a year.
* It pulled in a lot of dependencies, many of which were outdated. In
  particular, it locked the `http` gem to version 3.3, preventing us
  from upgrading to 4.2.
* It raised exceptions on normal error conditions, like for deleted
  tweets or suspended users, which we really don't want.
* We had to wrap it to provide caching.

Changes:

* Fixes #4226 (Exception when creating new artists entries for suspended
  Twitter accounts)
* Drop support for scraping images from summary cards. Summary cards
  are the previews you get when you link to a website in a tweet. These
  preview images aren't always the best image.

app/logical/twitter_api_client.rb

@@ -0,0 +1,26 @@
+class TwitterApiClient
+  extend Memoist
+
+  attr_reader :api_key, :api_secret
+
+  def initialize(api_key, api_secret)
+    @api_key, @api_secret = api_key, api_secret
+  end
+
+  def bearer_token(token_expiry = 24.hours)
+    http = Danbooru::Http.basic_auth(user: api_key, pass: api_secret)
+    response = http.cache(token_expiry).post("https://api.twitter.com/oauth2/token", form: { grant_type: :client_credentials })
+    response.parse["access_token"]
+  end
+
+  def client
+    Danbooru::Http.auth("Bearer #{bearer_token}")
+  end
+
+  def status(id, cache: 1.minute)
+    response = client.cache(cache).get("https://api.twitter.com/1.1/statuses/show.json?id=#{id}&tweet_mode=extended")
+    response.parse.with_indifferent_access
+  end
+
+  memoize :bearer_token, :client
+end