A client can ebale screensharing by setting the isScreensharing
flag in the call parameters to TRUE. This change will only take into
effect if the call and the conference support video capabilities.
As far as the signalling is concerned, the SDK will add or modify the
content of the main video stream to "slides" if the call is in a
conference.

Screensharing can be enabled for any layout the client is in.

In case one or more clients wish to share the screen, the last one
making its request will actually share the screen.

The application has the responsability to set the video source
descriptor corresponding to the screen, window or program to share. This
can be done eithe rbefore or after updating the call parameters.
Similarly, once the video scharing session ends, the application must
change the video source descriptor.

The person who shared its screen can avoid sharing the image of its
camera by diabling the camera in the call parameters

The application will be notified if the screensharing request was
accepted through a dedicated callback

Assign label to local streams

Implement limit to number of thumbnail streams requested. In other word,
this limit applies to the participants whose role is speaker and they
send their video stream to the server only.
For example if the limit is 10 and in a conference there are 50
participants but only 10 that send their video stream to the conference
server, all clients will be requesting these 10 streams. However, once
another one turns its camera on, then all participant will send a
reINVITE to the conference server to stop receiving any thumbnail stream
The threshold can be configured by calling
linphone_core_set_conference_max_minature

Copy t= field from the offer
Split main and thumbnail stream availabilities
Ignore louder speaker callback as long as a participant is screensharing and notify me device that active speaker changed once the conference receives the confirmation that screensharing as been accepted
Correctly propagate start and end times to conference
Reset mLocalScreenSharingEnabled when the stream is inactive or no payload have been accepted
Improve reliability of Android Platform Helper

Do send automatic conference reINVITEs if RTP bundle mode is disabled
and do not offer thumbnail stream either. This will allow to have better
performances even if the user experience is worsened