Display assignment deadline on student's success page + UI polish for overall student assignment flow

[femmebot]

Problem

• While we provide teachers with the ability to assignment deadlines, we don't display the deadlines to students.
• Teachers reported that students skip the step where their identifier is associated with their GitHub handle because they lacked context and simply took the lazy route.
• The student assignment acceptance flow also contains the Classroom header which isn't useful to students and similar content/UI elements that don't make sense to students.

Proposed

Since students need to accept the assignment, we can display the deadline and other important assignment details on the success page. They can revisit the page by using the assignment link (until the teacher disables the invitation URL) to get more comprehensive, scannable assignment details:

• Include team name, if applicable
• Display deadline, if applicable
• Emphasized assignment details and de-emphasized note about the email invitation where no action was needed.

I removed the GitHub Classroom from all the student pages and rewrote/re-formatted the copy to help make things easier to scan for important details.

Before

After

[d12]

WOW these designs look crisp and clean. :sparkles: :sparkles: :sparkles: