Updated browserstack's client.
Prisoners can be as young as 15 years old.
* Moved _ad_help to the views/application directory to be reusable across the app.
* Added a form for editing prisoner's information.
* Added a guard around the logic in PrisonerDetailsController to ensure that the client
  has their cookies enabled.
* Moved helper methods to a ParamUtils module.

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* Added a blind stopper™ in a few places.

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* Added session initialisation to PrisonerDetailsController.

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* Moved views to deferred/visitors_details.

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* PrisonerDetailsController will now pass on the flow to VisitorsDetailsController.

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* Implemented a working Deferred::VisitorsDetailsController.
* Added additional tests for adding/removing visitors.

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* Added routes to prisoner details, visitor details, and slot selection.

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* I've generated Deferred::SlotsController.

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* Roughly moved all logic to Deferred::SlotsController.
* Updated redirection paths across the app.
* Moved corresponding templates to the new location.

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* Generated a skeletal Deferred::VisitsController.

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* Visit confirmation screen for deferred requests.
* Added routes.

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* Fixed service domain, to pass through a real domain.

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* Moved the visit helper method to the ApplicationController.

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* Moved more functional tests for Deferred::VisitorsDetailsController.

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* Cleared unused stuff out of VisitController.

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* Added guards around cookies and sessions to PrisonerDetailsController.

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* Moved cookie- and session- checking logic to a separate module and added inclusions
  to each controller.

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* Cleaned up routing using scopes and such.
* The /prisoner-details legacy entry point now redirects to /prisoner_details/edit.

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