Changed font of corner QR codes to 'Computer Concrete'

Ref: http://tex.stackexchange.com/questions/25249/how-do-i-use-a-particular-font-for-a-small-section-of-text-in-my-document

The old textboxes were needlessly big and bold
Merge pull request #432 from abhinavc/master

Changed font of corner QR codes to 'Computer Concrete'