Added media/qrcodes directory

This is where the generated QR codes will go.

References #3.
Modified apps.html to point at QR codes.

The template now supports QR codes.  Now to actually do them.
Added QR code support.

QR codes are generated as APKs are added or upgraded, and the web site
will display them.  The QR code generating code is also tested.
Merge branch 'feature/issue-3' into develop