Do not compile SAS relay feature by default

If a project needs these features then it should enable it explicitly and
edit the top level CMakeLists.txt file. See comment in that file.
Merge branch 'develop'
Compile x86 code
Change function name to avoid name clash with other libraries
Merge branch 'develop' - rename aes_init to avoid name clashes
NEWS and CMakeLists for V4.2.4
Add functions to read the 'secure since' field from cache
TIVI - change SDES wording to SDP/S
Add functions to set retry counters and cap time

An application may set retry counters and cap time depending on network
conditions. An application must take care regarding if the retries are too big
and if it suppresses RTP during ZRTP negotiation after the "Hello" phase.
Merge remote-tracking branch 'origin/develop' into ph-develop