Re-introduce "Send email to users" link in Admin area

This link was mistakenly removed during a CE-to-EE merge. We've added a
view spec to ensure it doesn't happen again!

Closes gitlab-org/gitlab-ee#222

CHANGELOG-EE

@@ -4,6 +4,9 @@ v 8.5.0 (unreleased)
   - Show warning when mirror repository default branch could not be updated because it has diverged from upstream.
   - More reliable wiki indexer
 
+v 8.4.4
+  - Re-introduce "Send email to users" link in Admin area
+
 v 8.4.3
   - Elasticsearch: fix partial blob indexing on push
   - Elasticsearch: added advanced indexer for repositories

app/views/admin/users/index.html.haml

@@ -30,6 +30,7 @@
 
   .gray-content-block.second-block
     .pull-right
+      = link_to 'Send email to users', admin_email_path, class: 'btn'
       .dropdown.inline
         %a.dropdown-toggle.btn{href: '#', "data-toggle" => "dropdown"}
           %span.light

spec/views/admin/users/index.html.haml_spec.rb

+require 'rails_helper'
+
+describe 'admin/users/index' do
+  it 'includes "Send email to users" link' do
+    assign(:users, User.all.page(1))
+
+    render
+
+    expect(rendered).to have_link 'Send email to users', href: admin_email_path
+  end
+end