Add triggerClass support to the popover menu

ui/app/components/popover-menu.js

@@ -15,6 +15,8 @@ const FOCUSABLE = [
 export default Component.extend({
   classnames: ['popover'],
 
+  triggerClass: '',
+
   isOpen: false,
   dropdown: null,
 

ui/app/templates/components/popover-menu.hbs

@@ -3,10 +3,10 @@
   @onOpen={{action (queue (action (mut isOpen) true) (action capture))}}
   @onClose={{action (mut isOpen) false}} as |dd|
 >
-  <dd.Trigger data-test-popover-trigger class="popover-trigger button is-primary" {{on "keydown" (action "openOnArrowDown" dd)}}>
+  <dd.Trigger data-test-popover-trigger class={{concat "popover-trigger button is-primary " triggerClass}} {{on "keydown" (action "openOnArrowDown" dd)}}>
     {{label}} {{x-icon "chevron-down" class="is-text"}}
   </dd.Trigger>
   <dd.Content class="popover-content">
-    {{yield}}
+    {{yield dd}}
   </dd.Content>
 </BasicDropdown>