Add conference version to Linphone specification. If no conference specification is provided, then predefined call subjects will not be allowed
    Predefined subjects:
           "Conference"
           "ICE processing concluded"
           "Refreshing"
           "Media change"
           "Call on hold"
           "Call on hold for me too"

    Parse account custom parameters in the linphonerc file

Prevent AccountParams.setOutboundProxyEnabled crash if called before setServerAddress in liblinphone

This saves time to establish the audio stream.
Starting before ICE verified was not a good idea: it will trigger retransmissions, and retransmission interval growing over time makes the handshake slower.
Also, fix an issue where callee sets host candidates as default candidates in SDP, sflrx must be preferred.
(ported from release/5.1)

Implement participant addition to active conference. The admin will send a REFER to the conference server and the new address will be dialed out

Using NDK r23c (LTS) instead of r20, updated mediastreamer2 to fix DEVICE_HAS_BUILTIN_AEC flag for devices that explicitely say otherwise

This reverts commit 6934f6c7.

Fix a crash on video conference when we got an old conference in log with no call ID.

revert this commit when yocto is updated

BCToolBox : add an insensitive case search function to replace std::find without having to deal with locale.