Merge branch 'fix-external-label-color' into 'master'

Add font color contrast to external label in admin area

## What does this MR do?
Adds a darker font color to `.label-default` so that the labels have more contrast

## Are there points in the code the reviewer needs to double check?
~~I used the same font color as the `.badge` on that same page but it was not listed as a variable in `variables.scss`. I'm not sure if both references need to be added as a sass variable or whether they should be replaced with an existing color in the variables list.~~

In reference to [Dmitriy's note about the colors](https://gitlab.com/gitlab-org/gitlab-ce/issues/20114#note_13251919), I changed the color to `$btn-transparent-color` and also took the liberty to change it on the navigation badges as well.

## Why was this MR needed?
Improves existing UI

## What are the relevant issue numbers?
Closes #20744 

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-09_at_2.49.04_PM](/uploads/df8f402cc1dd423a2c37c9f4067b95f8/Screen_Shot_2016-08-09_at_2.49.04_PM.png)

After:
![Screen_Shot_2016-08-09_at_3.32.54_PM](/uploads/396f6679618630cab7a40e432f259084/Screen_Shot_2016-08-09_at_3.32.54_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5743

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.12.0 (unreleased)
   - Add two-factor recovery endpoint to internal API !5510
+  - Add font color contrast to external label in admin area (ClemMakesApps)
   - Change merge_error column from string to text type
   - Reduce contributions calendar data payload (ClemMakesApps)
   - Add `web_url` field to issue, merge request, and snippet API objects (Ben Boeckel)

app/assets/stylesheets/framework/nav.scss

@@ -71,7 +71,7 @@
     .badge {
       font-weight: normal;
       background-color: #eee;
-      color: #78a;
+      color: $btn-transparent-color;
       vertical-align: baseline;
     }
   }
@@ -335,10 +335,6 @@
         }
       }
 
-      .badge {
-        color: $gl-icon-color;
-      }
-
       &:hover {
         a, i {
           color: $black;

app/assets/stylesheets/pages/admin.scss

@@ -96,6 +96,10 @@
       line-height: inherit;
     }
   }
+
+  .label-default {
+    color: $btn-transparent-color;
+  }
 }
 
 .abuse-reports {