PROPOSAL: use belledonne's sofia-sip repository

[pierigno]

hello,

I'd like to make you aware of the existence of the belledonne's fork
of sofia-sip code repository, which is a well maintained, drop-in
replacement for current, abandoned sofia-sip used by (kde-)telepathy
and for which fixes a few bugs.

The code is reachable at
https://github.com/BelledonneCommunications/sofia-sip, works with no
problem with rakia.

regards,
Pierangelo