[Packaging] Missing Opus support

[Nightfall]

On Kubuntu 15.04 (up-to-date) and the current 16.04 daily (live system) SFLphone is missing Opus support (it is not shown in the account settings' codecs list) although according to [1] Opus support has been implemented for some years already.

[2] lists libopus-dev in the daemon's build dependencies - it's missing in the sflphone package's Build-Depends though.

Building the daemon from source (apt-get source sflphone; build the daemon; checkinstall it; adjust DBus service file) with libopus-dev installed creates an additional file libcodec_opus.so (compared to a package created without libopus-dev installed) and an opus entry becomes available in the codecs list.

So, libopus-dev should be added to the build dependencies. I don't know if libopus0 is necessary as an additional (non-build) package dependency.

[1] https://projects.savoirfairelinux.com/issues/14602
[2] https://projects.savoirfairelinux.com/projects/sflphone/wiki/Debian-based

Package versions on 15.04:

# vv Missing Opus support vv
sflphone-daemon:
  Installed: 1.4.1-0.1ubuntu1
  Candidate: 1.4.1-0.1ubuntu1
  Version table:
 *** 1.4.1-0.1ubuntu1 0
        500 http://de.archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
        100 /var/lib/dpkg/status

sflphone-kde:
  Installed: 1.4.1-0.1ubuntu1
  Candidate: 1.4.1-0.1ubuntu1
  Version table:
 *** 1.4.1-0.1ubuntu1 0
        500 http://de.archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
        100 /var/lib/dpkg/status

libopus-dev:
  Installed: 1.1-0ubuntu2
  Candidate: 1.1-0ubuntu2
  Version table:
 *** 1.1-0ubuntu2 0
        500 http://de.archive.ubuntu.com/ubuntu/ vivid/main amd64 Packages
        100 /var/lib/dpkg/status