Bug 1035670 - [BB] Create new shared component to manage icon fonts

@pivanov I've been using http://icomoon.io/app to generate the font and ´:before´ is their default option when generating the css. Also in Settings app where I did the first patch to replace icons is also using ´:before´.
I guess in all apps will have to solve this issues depending on how the use pseudo-elements.
Active state for lists BB is using ´:after´ so there's no collision there.