Prepare the SDK for the new Flexisip build and packaging scripts

• Parent : flexisip!540 (merged)

• BC/public/external/srtp!7 (merged)

• bctoolbox!116 (merged)

• bcunit!13 (merged)

• belle-sip!203 (merged)

• belr!33 (merged)

• liblinphone!1428 (merged)

• mediastreamer2!478 (merged)

• ortp!75 (merged)