[Fix #1096] task to delete old accounts

lib/tasks/2017_12_20_delete_old_administration.rake

@@ -0,0 +1,8 @@
+namespace :'2017_12_20_delete_old_administration' do
+  task set: :environment do
+    Administration.all.each do |a|
+      puts "Deleting #{a.email}"
+      a.destroy
+    end
+  end
+end