Update spacing for checkbox and panel

@hazelyang metrics,
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1519#note_26863100

app/assets/javascripts/projects/settings_service_desk/components/service_desk_setting.js

@@ -42,6 +42,7 @@ export default {
   },
 
   template: `
+    <div>
       <div class="checkbox">
         <label for="project_service_desk_enabled">
           <input
@@ -55,9 +56,10 @@ export default {
             Activate service desk
           </span>
         </label>
+      </div>
       <template v-if="isActivated">
         <div
-          class="panel panel-default">
+          class="panel-slim panel-default">
           <div class="panel-heading">
             <h3 class="panel-title">
               Forward external support email address to:

app/assets/stylesheets/framework/panels.scss

-.panel {
-  margin-bottom: $gl-padding;
-
+@mixin panel {
   .panel-heading {
     padding: $gl-vert-padding $gl-padding;
     line-height: 36px;
@@ -48,3 +46,14 @@
     line-height: inherit;
   }
 }
+
+.panel {
+  @include panel;
+  margin-bottom: $gl-padding;
+}
+
+.panel-slim {
+  @extend .panel;
+  @include panel;
+  margin-bottom: $gl-vert-padding;
+}