Merge branch 'dennis-positioning-important' into 'master'

Designate common positioning classes as `!important` a la Bootstrap

See merge request gitlab-org/gitlab-ce!26621

app/assets/stylesheets/framework/common.scss

@@ -462,10 +462,10 @@ img.emoji {
 }
 
 /** COMMON POSITIONING CLASSES */
-.position-bottom-0 { bottom: 0; }
-.position-left-0 { left: 0; }
-.position-right-0 { right: 0; }
-.position-top-0 { top: 0; }
+.position-bottom-0 { bottom: 0 !important; }
+.position-left-0 { left: 0 !important; }
+.position-right-0 { right: 0 !important; }
+.position-top-0 { top: 0 !important; }
 
 .drag-handle {
   width: 4px;