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

This is the same as the canonical `RegistrationsController#cancel`, but I don't know if we can add anything specific here to better explain this action.