Implement OneTrust Snippet on Developer Site

Closes #11 (closed)

• Adds OneTrust to developer.gitlab.com ("Cookie Preferences" link in the footer)
• Adds Privacy Policy link
• Adjusts footer styling for small-width screens (so all the links fit)

Before	After
Large screens
	California version:
Small screens
n/a
n/a

The banner in the last image here only comes up if you're in regions listed as having a banner in this comment.