FEATURE: image uploads now have short urls

Shorten all image uploads to use short urls, this is the client
side implementation.

app/serializers/upload_serializer.rb

@@ -1,5 +1,11 @@
 class UploadSerializer < ApplicationSerializer
-
-  attributes :id, :url, :original_filename, :filesize, :width, :height
-
+  attributes :id,
+             :url,
+             :original_filename,
+             :filesize,
+             :width,
+             :height,
+             :extension,
+             :short_url,
+             :retain_hours
 end