Feature/structure interface (#4)

* Moves mixins in docs folder

* Adds class to UI components

* Fix naming convenction

* Adds autoprefixer also in dev mode

* Updates info

* Renames palette

* Adds base template for docs pages

* Moves docs index page

* Improves footer markup. Disables categories and js includes (not necessary now)

* Improves typography sizes according to the viewport

* Renames method

* Adds new includes in the ITCSS pyramid

* Improves the docs style by adding a new layout structure and the side navigation

* Adds UI style

* Icons source file

* Updates icons

* Adds some versions of the Fullstack Bulletin logo

* Other small improvements

Author: lmammino