Merge branch 'css-refactoring' into 'master'

Small css improvements

See merge request !1450

app/assets/stylesheets/gl_bootstrap.scss

 /*
  * Twitter bootstrap with GitLab customizations/additions
  *
- * Some unused bootstrap compontents like panels are not included.
- * Other components like tabs are modified to GitLab style.
- *
  */
 
 $font-size-base: 13px !default;

app/assets/stylesheets/main/mixins.scss

@@ -139,7 +139,7 @@
 }
 
 @mixin panel-colored {
-  border: none;
+  border: 1px solid #EEE;
   background: $box_bg;
   @include box-shadow(0 1px 1px rgba(0, 0, 0, 0.09));