DEV: Remove gifsicle dependency (#10357)

Dependency on gifsicle, allow_animated_avatars and allow_animated_thumbnails
site settings were all removed. Animated GIF images are still allowed, but
the generated optimized images are no longer animated for those (which were
used for avatars and thumbnails).

The added 'animated' is populated by extracting information using FastImage.
This field was used to selectively reoptimize old animations. This process
happens in the background.

app/models/upload.rb

@@ -78,7 +78,6 @@ class Upload < ActiveRecord::Base
   def create_thumbnail!(width, height, opts = nil)
     return unless SiteSetting.create_thumbnails?
     opts ||= {}
-    opts[:allow_animation] = SiteSetting.allow_animated_thumbnails
 
     if get_optimized_image(width, height, opts)
       save(validate: false)
@@ -86,7 +85,9 @@ class Upload < ActiveRecord::Base
   end
 
   # this method attempts to correct old incorrect extensions
-  def get_optimized_image(width, height, opts)
+  def get_optimized_image(width, height, opts = nil)
+    opts ||= {}
+
     if (!extension || extension.length == 0)
       fix_image_extension
     end
@@ -461,11 +462,12 @@ end
 #  secure                 :boolean          default(FALSE), not null
 #  access_control_post_id :bigint
 #  original_sha1          :string
-#  verified               :boolean
 #  verification_status    :integer          default(1), not null
+#  animated               :boolean
 #
 # Indexes
 #
+#  idx_uploads_on_verification_status       (verification_status)
 #  index_uploads_on_access_control_post_id  (access_control_post_id)
 #  index_uploads_on_etag                    (etag)
 #  index_uploads_on_extension               (lower((extension)::text))