install-autotest-server.sh: Add support to install on Debian.

Signed-off-by: Rudá Moura <rmoura@redhat.com>
web frontend: Use django.contrib.staticfiles to deliver static content

frontend.wsgi now delivers both static (/media/) and dynamic content,
by using django.contrib.staticfiles.handlers.StaticFilesHandler and
STATIC_URL setting, so we can remove ADMIN_MEDIA_PREFIX due its deprecation,
starting from Django 1.3. Fix issue #743.

Signed-off-by: Rudá Moura <rmoura@redhat.com>