Spike add password change decoration for authentication token renewal

[gonzalo-bulnes]

As a developer
In order to get an insight of which way could lead to effectively decorating the Devise::PasswordsController#update action
And to be able to decide which is the better way to write the corresponding RSpec example
I want to explore some of the possible implementations

This spike is part of #40.

[gonzalo-bulnes]

Relevant Devise code:

• the Devise::PasswordsController of course
• the reset_password_by_token method which identifies which user (more generally: resource) must be given a new authetication token
• in case the password update should be faked in the RSpec example, the instruction which generates the resource reset_password_token.
  Do notice that this token has no relation with token authentication but is required to identify the resource which should be updated