#2935 Re-add G.729 as all patents have expired

[Alexander Rath]

In early 2017 all relevant patents on G.729 have expired. As it is now public domain, it can be implemented and used without any license fees. Up to r2174 G.729 was already part of CSipSimple but then removed because of the patents that are now expired. Please add it again, as it is the most accepted highly compressed Codec in VoIP.
https://www.mgraves.org/2017/03/its-official-the-patents-on-g-729-have-expired/