New layout for instructor pages

The layout of instructor pages and navigation bars has been massively improved by Tim Bretl.

Easy switching. You can now quickly switch between different courses and different instances (semesters/terms) of a course. To do this, click on the downwards-pointing triangle to the right of the course name or instance name in the top navigation bar.

Shortcut tabs in the top menu bar. All pages can be accessed from the second-level tab bar, but for commonly used pages like "Questions" and "Assessments" there are also shortcut buttons in the top navigation bar.

Wide view on instructor pages. All instructor pages now use the full width of the web browser window. This is particularly helpful on pages like the Questions list, where there are many columns in a table. Student pages have not changed width and there is no plan to ever change this. When previewing a question in instructor mode, the width is fixed to the same as student view so questions always look the same for everyone.