Open "View Live Version" and "Preview Changes" in a new window

STUD-2058

cms/templates/container.html

@@ -87,12 +87,12 @@ templates = ["basic-modal", "modal-button", "edit-xblock-modal",
             <ul>
                 % if is_unit_page:
                     <li class="action-item action-view nav-item">
-                        <a href="${published_preview_link}" class="button button-view action-button is-disabled">
+                        <a href="${published_preview_link}" class="button button-view action-button is-disabled" rel="external">
                             <span class="action-button-text">${_("View Live Version")}</span>
                         </a>
                     </li>
                     <li class="action-item action-preview nav-item">
-                        <a href="${draft_preview_link}" class="button button-preview action-button is-disabled">
+                        <a href="${draft_preview_link}" class="button button-preview action-button is-disabled" rel="external">
                             <span class="action-button-text">${_("Preview Changes")}</span>
                         </a>
                     </li>

common/test/acceptance/tests/test_studio_container.py

@@ -692,6 +692,7 @@ class UnitPublishingTest(ContainerBase):
         Goes to the published version, then waits for the browser to load the page.
         """
         unit.view_published_version()
+        self.assertEqual(len(self.browser.window_handles), 2)
         self.courseware.wait_for_page()
 
     def _verify_and_return_staff_page(self):