Callbacks now have access to screen notification

```
Paratrooper::Deploy.new('amazing-app') do |deploy|
  deploy.add_callback(:before_setup) do |output|
    output.display("Disabling newrelic ping")
    # code to disable new relic
    output.display("Yep, done did that!")
  end
end
```
Change migration_check code style to match others