Base Oracle Vagrant box on official one

There's an official Vagrant box for Oracle: https://github.com/oracle/vagrant-boxes/tree/master/OracleDatabase. It still needs manual downloading of the installer, but then it installs Oracle directly within the VM instead of using Docker as our current box. So the set-up is a fair bit simpler. It seems we could just use it as is, only our custom setup scripts (user creation, sample data etc.) need to be provided.