Documentation: Guides have broken github icons in the footer.

[kcondon]

All guides in documentation have broken github icons in the footer:
This has happened before, was working in 4.4, broken in 4.5, must use browser like Chrome to see broken image, FF hides it.

[mheppler]

Possibly a symptom related to issue #3181. Will investigate locally.

[mheppler]

Fixed URL ref to githubicon.png which was displaying as a broken img in the guides footer. Resized image file (512px) to be smaller (96px).

Code checked into the 3181-guides-build-warning branch.

[mheppler]

Made copyright year in guides footer dynamic. d8f1b98

Related to #2905

[kcondon]

The icons are fixed but cannot test the footer date since I cannot adjust the system date on the build machine @mheppler @pdurbin please test on your dev boxes thanks.

[mheppler]

With the direction of @pdurbin, fudged date to test copyright locally.

[pdurbin]

Still broken as of 9f93e7b on the homepage for the docs at least.

[pdurbin]

I'm proposing a fix in 74d6846 (pull request #3394) that uses an absolute rather than relative path. It relies on the fact that we create a symlink called "latest". That is to say the GitHub icon is at http://guides.dataverse.org/en/latest/_static/images/githubicon.png . Passing to QA.