Add possibility to Bulk Delete Topic Sections

Test removal of empty sections Create a new course, and populate some of the sections with resources and activities. Ensure at least some sections are empty - containing no activities or resources. Turn editing on. Select the 'delete empty sections' options at the bottom of the course page. In the modal dialog that appears, confirm the deletion with 'Delete all empty sections'. Check that all empty sections have been removed from the course. No sections containing resources or activities should have been removed (or reordered).