Added elinux and GSoC registry links to Previous contribution

See merge request gsoc/gsoc.beagleboard.io!11

Point to the GSoC section of the forum. It'll be less intimidating than
the overall forum.

This reverts commit 2ab845b9.

Don't love it.

This reverts commit f7c822be.

Unfortunately, the load time was unacceptable because the YouTube embed
is heavy.

This is feedback for gsoc/gsoc.beagleboard.io!11 (comment 17242)

It feels to me like having these on separate pages makes for a lot of
clicking. I think scrolling is better than clicking.