Adds support for the IETF Opus codec (patch by Boris Grozev). Fixes a problem that prevented Jitsi from using formats that are disabled by default (pach by Boris Grozev)

Applies a patch from Boris Grozev that allows setting different codec configurations to different accounts. It is now possible to set entirely different codec preference for every account.

Commits an initial version of the libjitsi library which should be fully functional with respect to neomedia/MediaService and should be usable with and without OSGi.