Use Ubuntu 14.04 for charms by default

Ubuntu 14.04 (Trusty Tahr) is the new Long Term Support version, so it makes sense to
use it instead of Ubuntu 13.04 (Raring Ringtail) which has been
unsupported(no more updates) for 3 months now.
Install gpac from the Ubuntu repositories

Instead of downloading a .deb of gpac from the official website, use the
Ubuntu repositories by default. The official .deb are not compatible
with Ubuntu 14.04, and Ubuntu 14.04 already has a recent version of gpac
in the repositories.
Replace PPA used to get FFmpeg

jon-severinsson FFmpeg PPA does not work on Trusty currently, so use my
PPA with a working FFmpeg.
Remove use of FFmpeg -sameq option

This option no longer exists, see
<https://www.ffmpeg.org/faq.html#Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f>
Fix Apache setup

Orchestra/Webui:
- The default site is now called 000-default, so replace calls to
  "a2dissite default" by "a2dissite 000-default".
- a2ensite now requires site files to end with .conf to work
Publisher:
- overwrite 000-default.conf and default-ssl.conf instead of default and
  default-ssl
Fix glusterfs volume creation

Fix the following error message with glusterfs on Trusty:
    volume create: medias_volume_0: failed: The brick
    oscied-local-machine-5:/mnt/bricks/exp0 is is being created in the
    root partition. It is recommended that you don't use the system's root
    partition for storage backend. Or use 'force' at the end of the command
    if you want to override this behavior
OrchestraHooks.py: do not delete the rabbitmq vhost /

This does not seem to have any purpose, and it breaks rabbitmq (with error
messages like {{{badmatch,{error,{no_such_vhost,<<"/">>}}}).