Merge branch 'winh-position-helpers' into 'master'

Add CSS helper classes for positioning

See merge request gitlab-org/gitlab-ce!24821

app/assets/stylesheets/framework/common.scss

@@ -420,3 +420,9 @@ img.emoji {
 .ms-no-clear ::-ms-clear {
   display: none;
 }
+
+/** COMMON POSITIONING CLASSES */
+.position-bottom-0 { bottom: 0; }
+.position-left-0 { left: 0; }
+.position-right-0 { right: 0; }
+.position-top-0 { top: 0; }