Removing redundant jobs page images

Discourage practice of adding 'OLD' variants of images in production
code.

Changes to be committed:
deleted:    images/jobs/jobs-bg@2xOLD.jpg
deleted:    images/jobs/jobs-bgOLD.jpg
Update Jobs background image

Background image was updated, and the primary navigation color was
changed to better suit the image.

Hero formatting modified to better match the hero background.

Changes to be committed:
modified:   _sass/pages/_about.scss
new file:   images/jobs/jobs-bg-small.jpg
new file:   images/jobs/jobs-bg-small@2x.jpg
modified:   images/jobs/jobs-bg.jpg
modified:   images/jobs/jobs-bg@2x.jpg
modified:   pages/jobs.html