Add Python 3.4 and Django 1.7, drop Python 2.6 and Django 1.5.
Change hashing to prevent collisions.

Previously, having albums or photos with the same names could result
in serving incorrect files. This was a security risk for people who
use the same naming scheme in every album.

Also use a MD5 instead of a SHA1 since it's shorter while still
sufficient to prevent collisions and enumeration attacks.
Django 1.5 isn't supported anymore.
Ignore a warning triggered by Django on Python 3.4.