Add volunteer credits page with requested content, links, images.

[membrq]

For issue #250 Add Volunteer Credits Page.

Completed:

• Added requested content, embedded links, and images/logos.

Had questions about a couple of issues:

• Image sizing for the logos and pictures on the volunteer page. For now, I've added static pixel sizes so images would match content length.
• Volunteers are not yet alphabetized. Wasn't sure if they should be sorted by first name or last name.

[richardwestenra]

Great work, thanks @membrq! I'll try to test this at some point soon, so we can get it merged promptly :)