Merge branch '22746-fix-admin-users-mobile-view' into 'master'

Resolve "Admin/Overview/Users mobile view"

## What does this MR do?

Fixes mobile layout issues on `/admin/users` page.

* Fixes control element placement when long usernames or email addresses overflow their container
* Fixes condensed dropdown menu (issue caused by acde2e30)

Before:
![Screen_Shot_2016-09-28_at_3.29.11_PM](/uploads/82cd27c367653beb29425065685274dd/Screen_Shot_2016-09-28_at_3.29.11_PM.png)

![Screen_Shot_2016-09-29_at_23.36.40](/uploads/e739638506388be9c5a0709e5f22b298/Screen_Shot_2016-09-29_at_23.36.40.png)

After:
![Screen_Shot_2016-10-24_at_11.55.32_PM](/uploads/ab6e49da85688d9fd2abc49de238a5bf/Screen_Shot_2016-10-24_at_11.55.32_PM.png)

## Are there points in the code the reviewer needs to double check?

Ensure css changes don't have any side effects elsewhere in GitLab.  (I don't think they would...)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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 it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #22746

See merge request !7087

CHANGELOG.md

@@ -6,6 +6,7 @@ Please view this file on the master branch, on stable branches it's out of date.
   - Prevent award emoji via notes for issues/MRs authored by user (barthc)
   - Adds an optional path parameter to the Commits API to filter commits by path (Luis HGO)
   - Fix extra space on Build sidebar on Firefox !7060
+  - Fix mobile layout issues in admin user overview page !7087
   - Fix HipChat notifications rendering (airatshigapov, eisnerd)
   - Add hover to trash icon in notes !7008 (blackst0ne)
   - Fix sidekiq stats in admin area (blackst0ne)

app/assets/stylesheets/framework/dropdowns.scss

@@ -15,6 +15,7 @@
 
     @media (max-width: $screen-xs-max) {
       width: 100%;
+      min-width: 240px;
     }
   }
 

app/assets/stylesheets/pages/admin.scss

@@ -80,10 +80,13 @@
     display: -webkit-flex;
     display: -ms-flexbox;
     display: flex;
+    white-space: nowrap;
   }
 
   .user-details {
     flex: 1 1 auto;
+    overflow: hidden;
+    padding-right: 8px;
   }
 
   .user-name {
@@ -91,6 +94,12 @@
     font-weight: 600;
   }
 
+  .user-name,
+  .user-email {
+    overflow: hidden;
+    text-overflow: ellipsis;
+  }
+
   .dropdown {
     .btn-block {
       margin-bottom: 0;