Add license key preview toggle

app/views/admin/licenses/_upload_trial_license.html.haml

@@ -15,6 +15,12 @@
             to enjoy GitLab Enterprise Edition Premium for 30 days.
           = form_for License.new, url: admin_license_path, html: { multipart: true, class: 'form-horizontal fieldset-form' } do |f|
             = f.hidden_field :data, value: license_key
+            %a{ href: '#hide-license', class: 'hide-license', id: 'hide-license' }
+              Show license key
+              = icon('chevron-down')
+            %a{ href: '#show-license', class: 'show-license', id: 'show-license' }
+              Hide license key
+              = icon('chevron-up')
             .well.trial-license-preview.prepend-top-15
               = license_key
             .modal-footer.form-actions