FIX: select-kit was in the wrong place

`app/` means we want to merge it into our application there. `addon`
means give it its own module namespace, which is what we wanted.

app/assets/javascripts/select-kit/addon/components/dropdown-select-box.js

@@ -0,0 +1,20 @@
+import SingleSelectComponent from "select-kit/components/single-select";
+
+export default SingleSelectComponent.extend({
+  pluginApiIdentifiers: ["dropdown-select-box"],
+  classNames: ["dropdown-select-box"],
+
+  selectKitOptions: {
+    autoFilterable: false,
+    filterable: false,
+    showFullTitle: true,
+    headerComponent: "dropdown-select-box/dropdown-select-box-header",
+    caretUpIcon: "caret-up",
+    caretDownIcon: "caret-down",
+    showCaret: false
+  },
+
+  modifyComponentForRow() {
+    return "dropdown-select-box/dropdown-select-box-row";
+  }
+});