Check if there are conflicts on master when running the build

- This is taken from
  https://github.com/alphagov/specialist-publisher/commit/9a097249c142c6e7146706dfd5fc0282c92f4886, as a thing discussed in tech lead standup that could be useful and passed to me to do via Jamie.
Remove the entire model layer

We don't really need that, do we? Pfft, models!

(Note to industrious branch detectives: this commit is designed to
engineer a merge conflict with master in the quickest way I could think
of.)