Use django.contrib.staticfiles to deliver static content

Starting from a discussion on issue #743, 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 and many lines from the Apache configuration.

_Note that there is included a miscellaneous bug fix regarding the installation script and Debian, which is better to ignore, this time._

Thanks to @clebergnu and @lmr for help and support on this issue.