[QAE1037] Admin: read_only view of form

Review 'read only' version of the form

```
As a Admin 
I want to be able to see the forms (read only) but exactly as the user filling it in would see it
So that I can have 'read only' version of form
```

So, basicly implemented:
* ability for Admin to login in as user (via device's standart login bypass feature)
* Added standart 'disabled' attribute and 'read_only' css class for most html controls on form (input,s textarea, radio etc)
* Resticted access for admin to update/ create/ destroy actions in controller level
* Added basic Rspec test for it
```
  def set_passed
    if eligible?
      update_column(:passed, true)
    end
  end
```
eligible? calls 'questions' method:
```
  def eligible?
    self.class.questions.all? do |question|
      answer = answers && answers[question.to_s]
      answer_valid?(question, answer)
    end
  end
```

and I'm don't know why @questions is nil