Create controller generator for devise (rails generator devise:controllers users -c sessions)

### Step1 (Done)
Create controllers templates, and create controller generator to copy ALL templates to rails app directory

### Step 2 (Done)
Create specific controllers using params provided by user, for example:
```ruby
rails generate devise:controllers users -c sessions confirmations
```

### Step 3 (Done)
Write tests

As this code is meant to be a simple example, maybe just ` devise_parameter_sanitizer.for(:sign_up) << :attribute` (without the `each`). is enough to show what kind of code these methods should have.