Dev jony

added wall:

spec/factories/walls.rb

spec/models/wall_spec.rb

db/migrate/20141003011707_create_walls.rb

app/models/wall.rb

Why did you use model here? it should be:

```ruby
let(:wall) { build(:wall) }
```

Maybe I should try to give you one more introduction of tests and explain why we do this and how to use factories!