Class stream, banners, and announcements

What changed

• A teacher's class page now opens on a Stream tab, next to Classwork, People, and a new Grades tab. A banner at the top shows the class name, section, and class code.
• Teachers can post announcements to the stream and pick a banner theme for each class. The stream also lists upcoming work by due date.
• A class can be renamed from its card or by clicking its title on the class page.