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

app/models/s3_region_site_setting.rb

@@ -6,12 +6,11 @@ class S3RegionSiteSetting < EnumSiteSetting
   end
 
   def self.values
-    @values ||= valid_values.sort.map {|x| {name: x, value: x} }
+    @values ||= valid_values.sort.map { |x| { name: x, value: x } }
   end
 
   def self.valid_values
-    [ '',
-      'us-east-1',
+    [ 'us-east-1',
       'us-west-1',
       'us-west-2',
       'us-gov-west-1',