MDL-56429 theme: add margin to processor settings form controls

Add a top margin to the form controls in the processor settings modal on
the notification preferences page to separate the content from the
controls.

message/templates/preferences_processor.mustache

@@ -51,7 +51,7 @@
     </div>
     <form>
         {{{formhtml}}}
-        <div class="form-actions">
+        <div class="form-actions m-t-1">
             <button type="submit" class="btn btn-primary">{{#str}} savechanges {{/str}}</button>
             <button type="button" class="btn" data-cancel-button>{{#str}} cancel {{/str}}</button>
         </div>