FEATURE: generate (avatar) thumbnails in a background task

FIX: keep the "uploading..." indicator until the server replies via the MessageBus
FIX: text was disapearing when uploading an avatar

PERF: always use a region for S3 (defaults to 'us-east-1')
FEATURE: ApplyCDN middleware when using S3
FIX: use the same pattern to store files on S3 and locally
PERF: keep a local cache of uploads when generating thumbnails
FEATURE: migrate_to_s3 rake task

db/migrate/20150525151759_set_default_s3_region.rb

@@ -0,0 +1,13 @@
+class SetDefaultS3Region < ActiveRecord::Migration
+  def up
+    execute <<-SQL
+      UPDATE site_settings
+         SET value = 'us-east-1'
+       WHERE name = 's3_region'
+         AND LENGTH(COALESCE(value, '')) = 0
+    SQL
+  end
+
+  def down
+  end
+end