Extend utility classes for `gitlab-ui`search-box

As noted in gitlab-ui!181 (comment 144661051) and gitlab-ui!181 (comment 144622633) we need to add two additional reusable utility classes to our CSS which are required mainly by the new search component.

  • gl-pl-8: This gives us a padding-left: 64px
  • gl-pr-8: This gives us a padding-right: 64px
  • pointer: Adds a cursor: pointer

/cc @winh

Edited by Martin Wortschack