remove uniqueness validation for app

The idea is that I'm using 

```
class Project < ActiveRecord::Base
  has_many :rapns_apps, class_name: 'Rapns::App', dependent: :destroy
end
```

And I do want to have same name in a project scope.
Rails doesn't provide a neat way to skip validation or modifying them in an inherited class, lets say.
So maybe a good idea is to disable it. I mean, I don't see the advantages.

I'm open to discussion regarding this. Maybe this is only my opinion.

N