This patch updates both the packaging files and the dockerfiles to
remove unused dependencies and add dependencies which can be installed
from the system instead of being built from contrib.

- remove libsrtp
- add jsoncpp
- add libupnp
- add libav related packages for Ubuntu 16.04, since it's recent enough
  to use the packaged version

Change-Id: I5b3432f15582c3f8170a580a8e783bec33a98c05
Tuleap: #823