Issue #3545499 by jessebaker, mred9: Add "Pages" navigation to Side Menu

Closes #3545499

This resolves the issue seen in comment #9 https://www.drupal.org/project/canvas/issues/3545499#comment-16262652

I have centralised the call to e.stopPropagation on our context/dropdown menus because it keeps not being added and causing similar issues. Issues like clicking on items in the dropdown, clicking the dropdown itself or (as was the case in this issue) clicking on dialogs spawned from context menus would simultaneously fire a click event on the dom element that spawned the menu.

In this issue, the dropdown menu was spanwed from a SidebarNode representing a Page. Clicking the Page, navigates you to the page. Thus clicking anywhere in the Delete Page dialog would also navigate you to the page. So when clicking the delete button it would both delete the page AND navigate you to the page you just deleted, hence a 404.