Encapsulate dependencies on Devise (refactoring)

**As a** developer 
**In order to** make dependencies transparent 
**And** to make the code testable in spite of them 
**I want** all dependencies to be properly encapsulated 
**And** I want them to be injected in the methods that use them 

Let's start with the (numerous) dependencies on Devise methods.

While doing that:
**In order to** make the code mode readable 
**And** to make modifications easier 
**I want** methods to be short 
**And** their names to be descriptive