Resolve "Add font-awesome to design.gitlab.com"

As issue #357 (closed) mentions we need font awesome to be consistent with gitlab-ui.

Since it's a temporary change I see no additional problems with versions of font-awesome out-of-sync between gitlab-ui and design.gitlab.com - it's unlikely that we will bump this version within nearest milestones and we should get rid of font-awesome both from gitlab-ui and this repo as soon as icon component is in place

Closes #357 (closed)