Squashed commit of the following:

commit f8708c263154910144b4f12497b2f2c93fcedadc
Author: Gabriel <edomadriz@gmail.com>
Date:   Sat Sep 27 18:04:23 2014 -0600

    User uniqueness validations and exception raise

commit 7a0ee24c459eb9cb9f977641e4b4c79f87fa4c02
Author: Gabriel <edomadriz@gmail.com>
Date:   Sat Sep 27 17:07:26 2014 -0600

    Add favorites without controller and change index, show and create for users pending validation for unique fb_id

commit d414143605f0e7ceb17309a0d9dd2cd9d0aa35d2
Author: Gabriel <edomadriz@gmail.com>
Date:   Sat Sep 27 14:28:56 2014 -0600

    Tabla favorites con nombre incorrecto por has_and_blongs_to_many