Add links to Part 2 and Part 3 of Systematic Program Design on edX

[nikty]

Currently the course page only lists link to the first part of the course series.
Even though it seems that the linked course contains all the information from all 3 parts, I noticed some differences

• Week 8's Design Quiz is missing in Part 1; instead stub question is shown
• Week 8's Quiz is present in Part 3

It is probably not that important, but I think it would be nice to have all these links on the course page insted of just the first one:

• https://courses.edx.org/courses/course-v1:UBCx+SPD1x+2T2015/course/
• https://courses.edx.org/courses/course-v1:UBCx+SPD2x+2T2015/course/
• https://courses.edx.org/courses/course-v1:UBCx+SPD3x+3T2015/course/