Federate header images, fix open-uri http->https redirection error

db/migrate/20170318214217_add_header_remote_url_to_accounts.rb

@@ -0,0 +1,5 @@
+class AddHeaderRemoteUrlToAccounts < ActiveRecord::Migration[5.0]
+  def change
+    add_column :accounts, :header_remote_url, :string, null: false, default: ''
+  end
+end