Refactor the files_controller.rb to use the strong parameters pattern.

[euler-room]

The Files controller is not vetting incoming parameters. They are accessed throughout the file using params[:my_param]. This raises a some security concerns.

Acceptance Criteria:

• Creates an action specific strong parameter method for each action:

def my_action_params
  params.permit(:id, :path, :etc)
end

• Removes all instances of params[:blah_blah]
• Loads params into the appropriate variable type for its use case (instance, local, etc)
• Passes variables into shared methods