Use Hashie for Strong parameter sanitization.

This pull request fixes an issue where exporting fails whilst running inside a rails application that has unpermitted params set to raise
i.e. 
```ruby 
config.action_controller.action_on_unpermitted_parameters = :raise
```
Rather than use strong parameters to sanitize params, this pull request introduces hashie. Using hashie we can define a list of keys that we expected to recieve, anything else will raise an error (Quite similar to Strong Params).

I'm forgetting how ruby works here. Will `owner` on the rhs of this statement resolve to the instance variable, `@owner`?