Demo enhancements

Fix table name in migration. 
Change file name for helper method. 
~~Remove Dockerfile~~ - we are going to use the STI build, where bundle install is ran automatically, als the app is ran all after the content is copied in a temporary directory. Keep also the Docker file, we want it to run on STI and Docker.

Question: Do we want to use [puma](https://github.com/openshift/ruby-20-centos/blob/master/.sti/bin/run#L23)? I think we can just use the default server with `config.ru`.