add preferences and customization (#171)

app/models/user.rb

@@ -17,6 +17,9 @@
 class User < ApplicationRecord
 
   before_create :set_encrypted_id
+  has_attached_file :background
+  validates_attachment :background,
+                       :content_type => { :content_type => ["image/jpg", "image/jpeg", "image/gif", "image/png"] }
 
   def self.from_omniauth(auth_hash)
     user = find_or_initialize_by(uid: auth_hash['uid'], provider: auth_hash['provider'])