Updated Course End Date info

To be more specific about end dates and certificates.

https://edx-wiki.atlassian.net/secure/RapidBoard.jspa?rapidView=110&view=detail&selectedIssue=DOC-298
How about this:

After grades and certificates are finalized, all students see the following information on their dashboards:

- The student's final grade, as a percentage.
- The grade, or percentage, necessary to earn a certificate. **(SP: Note that we need an updated screen shot for this; the current one doesn't show the grade required for a certificate.)**

(screen shot)

Additionally, students who have earned a certificate see a **Download Your Certificate (PDF)** button.

(screen shot) **(SP: Need a screen shot that shows the certificate button + the "grade required for a certificate" text.)**