- clients send a reINVITE with the desired stream based on their choice of layout upon reception of:
  - full notify state
  - participant added
  - participant removed
- change of layout (via conference params update or setLayout method) triggers a reINVITE from the client with the new desired streams
- server sends reINVITEs to clients only to notify them that they joined a conference. If the client calls a conference URI, no reINVITE from the server is sent

Add conference available media changed callback
Conference layout renaming: None -> Legacy
Add linphone_core_create_conference_params_2 in order to create conference parameters from an existing set
Split local conference tester to speed up test run
Rename testers Audio Conference (Basic) -> Audio Video Conference (Basic) and Audio Conference (Advanced) -> Audio Conference
Add media direction to string function