Harden edit elements feature spec

There is JS involved opening the dialog, so we
need to tell Capybara to wait for it.

spec/features/admin/edit_elements_feature_spec.rb

@@ -62,13 +62,17 @@
         end
       end
 
-      scenario "the add button opens add element form with the clipboard tab" do
+      scenario "the add button opens add element form with the clipboard tab", :js do
         visit alchemy.admin_elements_path(page_version_id: element.page_version_id)
         button = page.find(".add-nestable-element-button")
         expect(button).to have_content "Add Slide"
         button.click
-        expect(page).to have_select("Element")
-        expect(page).to have_css("[panel='paste_element_tab']")
+
+        expect(page).to have_css(".alchemy-dialog")
+        within ".alchemy-dialog" do
+          expect(page).to have_select("Element")
+          expect(page).to have_css("[panel='paste_element_tab']")
+        end
       end
     end
 
@@ -92,8 +96,11 @@
 
         scenario "the add button now opens add element form with the clipboard tab" do
           find("a.add-nestable-element-button").click
-          expect(page).to have_select("Element")
-          expect(page).to have_css("[panel='paste_element_tab']")
+          expect(page).to have_css(".alchemy-dialog")
+          within ".alchemy-dialog" do
+            expect(page).to have_select("Element")
+            expect(page).to have_css("[panel='paste_element_tab']")
+          end
         end
       end
     end
@@ -112,8 +119,9 @@
       button = page.find(".add-nestable-element-button")
       expect(button).to have_content "New element"
       button.click
-      expect(page).to have_select("Element")
+      expect(page).to have_css(".alchemy-dialog")
       within ".alchemy-dialog" do
+        expect(page).to have_select("Element")
         select2("Text", from: "Element")
         click_button("Add")
       end