Refactor pages with nested split views

There are a couple of pages — User grades and Learning plans — which use a nested split-view to navigate in tablet. This wasn't a good approach before, but now that we are going to add the swiping gesture it's even worse.

In grades, instead of just adding the new gesture, nested split views will be removed in favor of adding expandable items in the lists. These items will behave similarly to the expandable items in the new Course Index component in the LMS. One exception to this will be the grades view in tablet, given that it already contains all the information and the nested split view is redundant, so it'll be eliminated instead. Additionally, the title of a course grades page will display the name of the course instead of "Grades".

In learning plans, we intended to follow the same approach. But after finding some complications in the course tab (it already has some expanded information, but it's not complete), we decided to leave it as is for now and add swiping gesture.